CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 14/480,087 filed Sep. 8, 2014, which is a continuation of U.S. application Ser. No. 13/427,977 filed Mar. 23, 2012, which claims priority from Japanese Patent Application No. 2011-167450 filed Jul. 29, 2011. The entire contents of the above-noted applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an image-forming device provided with a cleaning unit such as a color laser printer. 
     BACKGROUND 
     There is known, as a color laser printer of an electrophotographic type, a tandem-type color laser printer provided with a plurality of photosensitive drums arranged in parallel in correspondence with toners of four colors of yellow, magenta, cyan, and black. 
     As such a tandem-type color laser printer, there is proposed a configuration in which a plurality of photosensitive drums are arranged in parallel above a belt unit having an endless intermediate transfer belt and are brought into contact with the intermediate transfer belt from above. 
     In the proposed configuration, the belt unit further includes a plurality of primary transfer rollers, a secondary transfer roller, and a cleaning unit. 
     The primary transfer rollers are arranged opposite to the corresponding photosensitive drums across the intermediate transfer belt. The secondary transfer roller is arranged on the downstream side relative to the downstream most primary transfer roller in the traveling direction of the intermediate transfer belt. The cleaning unit is arranged between the secondary transfer roller and the upstream most primary transfer roller in the traveling direction of the intermediate transfer belt. 
     When the intermediate transfer belt starts to travel in an image-forming operation, developer images of respective colors carried on the surfaces of the photosensitive drums are sequentially primary-transferred from the photosensitive drums onto the intermediate transfer belt. As a result, a color developer image is formed on the intermediate transfer belt. Thereafter, when the color developer image on the traveling intermediate transfer belt has reached a position opposite to the secondary transfer roller, a paper sheet is supplied between the secondary transfer roller and the intermediate transfer belt. As a result, the color developer image is secondary-transferred onto the paper sheet. The paper sheet onto which the color developer image has been formed is conveyed to a fixing unit, followed by fixing of the color developer image onto the paper sheet. 
     After completion of the secondary transfer of the color developer image onto the paper sheet, transfer residual toner remains on the peripheral surface of the intermediate transfer belt. When the transfer residual toner remaining on the surface of the traveling intermediate transfer belt has reached to a position opposite to the cleaning unit, the transfer residual toner is collected by the cleaning unit. The toner can also remain on the peripheral surface of the intermediate transfer belt when a patch test is performed. The cleaning unit is configured to collect not only the transfer residual toner but also residual toner generated by the patch test. 
     SUMMARY 
     However, in the above-proposed configuration, size reduction of the image-forming device is difficult. 
     That is, the cleaning unit needs to be arranged between the secondary transfer roller and the upstream most primary transfer roller in the travel direction of the intermediate transfer belt. On the other hand, a conveying path for conveying the paper sheet between the secondary transfer roller and the intermediate transfer belt is also formed around the secondary transfer roller. Therefore, a space for mounting the cleaning unit is restricted. 
     Further, the cleaning unit needs to have a certain capacity for storing waste toner collected from the intermediate transfer belt. Therefore, there is a limit to the size reduction of the cleaning unit itself. 
     Thus, arranging the cleaning unit between the secondary transfer roller and the upstream most primary transfer roller while ensuring the capacity of the cleaning unit without interfering with the conveying path inevitably leads to an increase in the size of the entire image-forming device. 
     In view of the foregoing, it is an object of the invention to provide an image-forming device capable of achieving size reduction while ensuring the capacity of the cleaning unit. 
     In order to attain the above and other objects, the invention provides an image forming device that may include: a photosensitive drum; a first roller; a second roller; an intermediate transfer belt; a transfer roller; a cleaner; a waste toner accommodating portion; and a paper guide. The intermediate transfer belt may be looped around the first roller and the second roller to circularly move in a moving direction. The intermediate transfer belt may be configured to contact the photosensitive drum. The transfer roller may be disposed opposite to the first roller with respect to the intermediate transfer belt. The cleaner may be configured to collect waste toner on the intermediate transfer belt. The cleaner may be disposed upstream of the photosensitive drum in the moving direction and downstream of the transfer roller in the moving direction. The waste toner accommodating portion may be configured to accommodate the waste toner collected by the cleaner. The paper guide may be configured to guide a recording medium and disposed between the cleaner and the waste toner accommodating portion. 
     According to another aspect, the present invention provides an image forming device that may include: a photosensitive drum; an intermediate transfer belt; a cleaner; a waste toner accommodating portion; and a paper guide. The intermediate transfer belt may be arranged in confrontation with the photosensitive drum. The cleaner may contact the intermediate transfer belt to collect waste toner on the intermediate transfer belt. The waste toner accommodating portion may be configured to accommodate the waste toner collected by the cleaner. The paper guide may be configured to guide a recording medium and disposed between the cleaner and the waste toner accommodating portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional side view of a color printer according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view of a drum unit shown in  FIG. 1  when viewed from the left-rear-upper side; 
         FIG. 3  is a perspective view of the drum unit shown in  FIG. 2  when viewed from the left-rear-upper side, where a left frame side plate is removed from the drum unit; 
         FIG. 4  is an enlarged cross-sectional view of a cleaning unit; 
         FIG. 5  is a cross-sectional side view showing an attachment/detachment operation of a plurality of developer cartridges; 
         FIG. 6  is a cross-sectional side view showing a housing operation of the drum unit; 
         FIG. 7  is a cross-sectional side view of a color printer according to a second embodiment of the present invention; and 
         FIG. 8  is a cross-sectional side view showing an attachment/detachment operation of a cleaning unit in the color printer shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     &lt;First Embodiment&gt; 
     1. Entire Configuration of Color Printer 
     As illustrated in  FIG. 1 , a color printer  1  (an example of an image-forming device) is a horizontally-placed intermediate transfer type color printer. 
     The color printer  1  includes a main casing  2 . The main casing  2  incorporates an image-forming section  3  and a paper feeding section  4  for feeding a paper sheet P to the image-forming section  3 . 
     (1) Main Casing 
     The main casing  2  is formed into substantially a rectangular box shape as viewed from side. A main body side opening portion  6  for communicating between the inside and outside of the main casing  2  is formed in one side wall of the main casing  2 . Further, a front cover  5  is provided in the same side wall of the main casing  2 . The front cover  5  is provided so as to be swingable about the lower end portion thereof between an opening position at which the upper end portion thereof is separated from the main casing  2  to open the main body side opening portion  6  and a closing position at which the upper end portion contacts the main casing  2  to close the main body side opening portion  6 . 
     Hereinafter, a side (right side of  FIG. 1 ) at which the front cover  5  is provided is defined as a “front side” of the color printer  1 , and the opposite side (left side of  FIG. 1 ) is defined as a “rear side”. The left and right sides are set with reference to the color laser printer  1  as viewed from the front side. In other words, the front side in the plane of  FIG. 1  is the left side, and the rear side in the plane of  FIG. 1  is the right side. 
     (2) Paper Feeding Section 
     The paper feeding section  4  includes a paper feeding tray  7  storing the paper sheets P. 
     The paper feeding tray  7  is detachably mounted on the bottom portion in the main casing  2 . A conveying path  8  extending from the rear end of the paper feeding tray  7  toward the image-forming section  3  (space between a belt unit  16  and a secondary transfer roller  24 , both of which will be described later) is formed in the main casing  2 . 
     The paper sheets P stored in the paper feeding tray  7  are picked up one by one by various rollers. The picked up paper sheet P is fed to the conveying path  8  and then to the image-forming section  3  along the conveying path  8 . 
     (3) Image-Forming Section 
     The image-forming section  3  is arranged above the paper feeding section  4  and includes an exposure unit  10 , a drum unit  15  (an example of a pull-out member), the belt unit  16 , and a fixing unit  17  (an example of a fixing member). 
     (3-1) Exposure Unit 
     The exposure unit  10  is disposed at the uppermost position inside the main casing  2 . The exposure unit  10  emits four laser beams corresponding to respective colors toward corresponding photosensitive drums  32  (to be described later). 
     (3-2) Drum Unit 
     The drum unit  15  is disposed inside the main casing  2  at a portion above the paper feeding section  4  and below the exposure unit  10 . The drum unit  15  is mounted so as to be slidable in the front-rear direction to a housing position (see  FIGS. 1 and 6 ) at which the drum unit  15  is housed in the main casing  2  and a pull-out position (see  FIG. 5 ) at which the drum unit  15  is outside the main casing  2  when the front cover  5  is opened. 
     The drum unit  15  includes four photosensitive drums  32  (an example of photosensitive members). Each of the four photosensitive drums  32  is rotatably supported about an axial line extending in the left-right direction. The four photosensitive drums  32  are arranged in parallel and spaced apart from each other so as to sequentially correspond to four colors of black, yellow, magenta, and cyan in the front-rear direction. 
     The drum unit  15  includes four scorotron chargers  33 . The four scorotron chargers  33  correspond respectively to the four photosensitive drums  32  and are each disposed on the upper-front side of the corresponding photosensitive drum  32 . 
     The drum unit  15  further includes four developer cartridges  31 . The developer cartridges  31  are arranged in parallel and spaced apart from each other in the front-rear direction. More specifically, a black developer cartridge  31 K, a yellow developer cartridge  31 Y, a magenta developer cartridge  31 M and a cyan developer cartridge  31 C are sequentially arranged from the front side toward the rear side. 
     Each developer cartridge  31  is detachably attached to the drum unit  15  and includes a developer frame  34 , a developing roller  36  housed in the developer frame  34 , a supply roller  37 , and a layer-thickness regulating blade  38 . 
     The developing roller  36  is rotatably supported by the developer frame  34  such that the lower side thereof is exposed from the developer frame  34 . The supply roller  37  is rotatably supported by the developer frame  34  so as to contact the developing roller  36  from above. The layer-thickness regulating blade  38  is supported by the developer frame  34  so as to be brought into press-contact with the developing roller  36 . The developer frame  34  includes, at a portion above the supply roller  37 , a toner accommodating portion  39  for accommodating toners of respective colors. 
     The drum unit  15  supports a cleaning unit  41 . The configuration of the cleaning unit  41  will be described later. 
     (3-3) Belt Unit 
     As illustrated in  FIG. 1 , the belt unit  16  is disposed inside the main casing  2  at a portion above the paper feeding section  4  and below the drum unit  15  set at the housing position. 
     The belt unit  16  includes a driving roller  20  (an example of a first roller), a driven roller  21  (an example of a second roller), an intermediate transfer belt  22  (an example of an endless belt), and four primary transfer rollers  23 . 
     The driving roller  20  and the driven roller  21  are arranged opposite to and spaced apart from each other in the front-rear direction. More specifically, the driving roller  20  is disposed spaced apart rearward from the rearmost photosensitive drum  32  by a distance equal to or more than the front-rear direction length of a first waste toner accommodating portion  44  (described later) of the cleaning unit  41 . The driven roller  21  is disposed frontward of the frontmost photosensitive drum  32  in the front-rear direction. 
     The intermediate transfer belt  22  is an endless belt spanned between the driving roller  20  and the driven roller  21 . The intermediate transfer belt  22  spanned between the driving roller  20  and the driven roller  21  forms a pair of straight planes extending in the front-rear direction. The four photosensitive drums  32  face the upper straight portion. The intermediate transfer belt  22  is circularly moved with the drive movement of the driving roller  20  and the driven movement of the driven roller  21  such that the upper portion thereof moves from the rear side toward the front side. 
     The primary transfer rollers  23  are arranged in parallel and spaced apart from each other in the front-rear direction. Each primary transfer roller  23  is opposite to the corresponding photosensitive drum  32  across the upper portion of the intermediate transfer belt  22 . 
     The secondary transfer roller  24  (an example of a transfer member) is disposed rearward of the belt unit  16 . 
     The secondary transfer roller  24  is opposed to the driving roller  20  of the belt unit  16  across the intermediate transfer belt  22  from the rear side so that the upper end thereof is disposed below the upper portion of the intermediate transfer belt  22 . 
     (3-4) Fixing Unit 
     The fixing unit  17  is disposed above the secondary transfer roller  24  and includes a heating roller and a pressure roller opposite to the heating roller. 
     (3-5) Image Forming Operation 
     (3-5-1) Developing Operation 
     The toner in the toner accommodating portion  39  is fed to the supply roller  37  and further to the developing roller  36 . 
     The toner that has been fed to the developing roller  36  is regulated in thickness by the layer-thickness regulating blade  38  with a rotation of the developing roller  36  and then carried on the surface of the developing roller  36  as a thin layer having a uniform thickness. 
     The surface of the photosensitive drum  32  is uniformly positively charged by the scorotron charger  33  with a rotation of the photosensitive drum  32  and, thereafter, exposed by laser beams emitted from the exposure unit  10 . As a result, an electrostatic latent image corresponding to an image to be formed on the paper sheet P is formed on the surface of the photosensitive drum  32 . 
     Further rotation of the photosensitive drum  32  causes the positively charged toner carried on the surface of the developing roller  36  to be fed to the electrostatic latent image formed on the surface of the photosensitive drum  32 . As a result, the electrostatic latent image formed on the photosensitive drum  32  is visualized, and a toner image resulting from reversal development is carried on the surface of the photosensitive drum  32 . 
     (3-5-2) Transfer/Fixing Operation 
     Toner images of respective colors that have been carried on the surfaces of the photosensitive drums  32  through the reversal development are sequentially primary-transferred onto the upper portion of the intermediate transfer belt  22  moving from the rear side to front side. As a result, a color image is formed on the intermediate transfer belt  22 . 
     At a timing when the color image reaches a portion at which the intermediate transfer belt  22  and the secondary transfer roller  24  are opposite to each other with the circulation of the intermediate transfer belt  22 , the paper sheet P is fed from the paper feeding section  4  to the opposing portion between the intermediate transfer belt  22  and secondary transfer roller  24 . Further circulation of the intermediate transfer belt  22  causes the color image to be secondary-transferred from the intermediate transfer belt  22  onto the paper sheet P. 
     Thereafter, the paper sheet P onto which the color image has been transferred is fed upward from the opposing portion between the intermediate transfer belt  22  and the secondary transfer roller  24 . Then, the paper sheet P passes through the cleaning unit  41  while being guided by a paper guide section  46  to be described later which is formed in the cleaning unit  41  and is then fed to the fixing unit  17  disposed above the cleaning unit  41 . 
     In the fixing unit  17 , the color image transferred onto the paper sheet P is subjected to heating and pressurization while the paper sheet P passes between the heating roller and the pressure roller to be thermally fixed onto the paper sheet P. 
     (4) Paper Ejection 
     The paper sheet P onto which the toner image has been fixed in the fixing unit  17  is ejected, by a paper ejection roller  40  formed in the upper portion of the main casing  2 , onto a paper ejection tray  11  formed on the upper surface of the main casing  2 . 
     2. Drum Unit 
     As illustrated in  FIGS. 2 and 3 , the drum unit  15  includes a drum frame  51  that collectively supports the four photosensitive drums  32  and the four scorotron chargers  33 . The drum frame  51  includes the four developer cartridges  31  detachably attached thereto. The drum frame  51  further includes the cleaning unit  41 . 
     (1) Drum Frame 
     The drum frame  51  is formed into substantially a rectangular frame shape having a bottom and integrally includes a pair of frame side plates  52  which are arranged opposite to and spaced apart from each other in the left-right direction and a frame front plate  53  connecting the front ends of the frame side plates  52 . 
     Each frame side plates  52  integrally includes a first side plate  55  and a second side plate  56 . 
     The first side plate  55  is formed into a flat plate shape extending in the front-rear direction and the up-down direction. The first side plate  55  has a front-rear direction width that is opposite to the frame front plate  53  and the four developer cartridges  31  in the left-right direction. 
     A first flange portion  57  that protrudes outward in the left-right direction is formed over substantially the entire front-rear width of the upper end of the first side plate  55 . A first inclined surface  58  is formed at the front end of the first flange portion  57  so as to be inclined upward toward the front. 
     The second side plate  56  is formed into a flat plate shape extending in the front-rear direction and the up-down direction. The second side plate  56  extends rearward from substantially the lower half portion of the rear end of the first side plate  55 . 
     A second flange portion  59  that protrudes outward in the left-right direction is formed over substantially the entire front-rear width of the upper end of the second side plate  56 . A second inclined surface  60  is formed at the front end of the second flange portion  59  so as to be inclined upward toward the front. 
     A handle portion  61  (see  FIG. 1 ) having substantially a U-like cross-section protrudes frontward from the frame front plate  53 . 
     (2) Developer Cartridge 
     Each developer cartridge  31  includes a box-shaped developer frame  34 . More specifically, as illustrated in  FIG. 1 , substantially the upper half of the developer frame  34  is formed into substantially a rectangular shape as viewed from a side and substantially the lower half thereof is formed into a tapered shape such that the rear side surface is inclined frontward toward the lower side. 
     Further, as illustrated in  FIG. 2 , the developer frame  34  has a left-right direction width slightly smaller than a distance between the frame side plates  52  of the drum unit  15 . Each developer cartridge  31  is detachably attached to between the frame side plates  52  of the drum unit  15 . 
     (3) Cleaning Unit 
     The cleaning unit  41  is disposed between the pair of second side plates  56  of the drum unit  15 . Further, as illustrated in  FIG. 1 , when the drum unit  15  is at the housing position at which the drum unit  15  is housed in the main casing  2 , the cleaning unit  41  is disposed rearward of the rearmost developer cartridge  31  at a portion above the secondary transfer roller  24  and below the fixing unit  17 . In other words, when being projected in the up-down direction, the cleaning unit  41  is disposed such that the front-rear direction center portion (the paper guide section  46  (described later), the rear end of the first waste toner accommodating portion  44  (described later) continuously provided from the front side of the paper guide section  46 , and the front end of a second waste toner accommodating portion  45  (described later) continuously provided from the rear side of the paper guide section  46 ) thereof overlaps the fixing unit  17 . 
     The front end (front end of the first waste toner accommodating portion  44  (described later)) of the cleaning unit  41  is formed into a tapered shape inclined downward toward the front. On the other hand, as described above, the rear side surface of each developer frame  34  is inclined frontward toward the lower side. The front end of the cleaning unit  41  is disposed below the developer frame  34  of the rearmost developer cartridge  31 C. That is, when being projected in the up-down direction, the front end of the cleaning unit  41  overlaps the developer frame  34  of the rearmost developer cartridge  31 C. 
     The cleaning unit  41  includes a casing  43  (an example of a frame). 
     The casing  43  includes the first waste toner accommodating portion  44 , the second waste toner accommodating portion  45  (an example of a treating member and a waste toner accommodating member) provided on the rear side relative to the first waste toner accommodating portion  44 , and a connection portion  81  ( FIGS. 2 and 3 ) connecting the first and second waste toner accommodating portions  44  and  45 . The paper guide section  46  (an example of a guide portion) allowing passage of the paper sheet P is formed between the first and second waste toner accommodating portions  44  and  45 . 
     (3-1) First Waste Toner Accommodating Portion 
     As illustrated in  FIG. 4 , the first waste toner accommodating portion  44  is formed into substantially a box shape extending from the lower-front side toward the upper-rear side with the front side lower end thereof opened. In the first waste toner accommodating portion  44 , a cleaning roller  42  (an example of a cleaning member), a metal roller  85 , a scraping member  86 , and a first conveying auger  87  (an example of a second conveying member) are accommodated. 
     The cleaning roller  42  is rotatably provided about an axial line extending in the left-right direction and supported by the first waste toner accommodating portion  44  such that a part of the peripheral surface thereof is exposed downward from the front end of the first waste toner accommodating portion  44 . 
     As illustrated in  FIG. 1 , when the drum unit  15  is at the housing portion, the cleaning roller  42  is positioned rearward of the rearmost photosensitive drum  32 . More specifically, the cleaning roller  42  is disposed so as to be brought into contact from above with the intermediate transfer belt  22  at a portion between the driving roller  20  and the rearmost photosensitive drum  32  in the circulation direction of the intermediate transfer belt  22 . 
     The metal roller  85  is, as illustrated in  FIG. 4 , rotatably supported at the both ends thereof by the both side walls of the first waste toner accommodating portion  44  so as to be brought into contact from the upper-rear side with the cleaning roller  42 . 
     The scraping member  86  is an elastically deformable blade plate, one end of which is supported by the first waste toner accommodating portion  44  and the other end of which elastically abuts against the peripheral surface of the metal roller  85 . 
     The first conveying auger  87  is rotatably disposed below the scraping member  86  about an axial line extending in the left-right direction. 
     The first conveying auger  87  includes an auger shaft whose both ends are rotatably supported by the both side walls of the first waste toner accommodating portion  44  and an auger blade formed around the auger shaft and helically extending in the left-right direction. 
     (3-2) Second Waste Toner Accommodating Portion 
     The second waste toner accommodating portion  45  is disposed spaced apart rearward from the first waste toner accommodating portion  44  and is formed into substantially a box shape, as viewed from a side, extending in the left-right direction. 
     The second waste toner accommodating portion  45  includes a partition  93  formed along the left-right direction below a second conveying auger  95  (to be described later). The partition  93  partitions the inner space of the second waste toner accommodating portion  45  into a conveying chamber  91  and a waste toner accommodating chamber  92 . A communication port  94  for communicating between the conveying chamber  91  and the waste toner accommodating chamber  92  is formed at the rear end of the partition  93 . 
     The conveying chamber  91  is defined as an upper space of the second waste toner accommodating portion  45 , in which the second conveying auger  95  is housed. The second conveying auger  95  extends in the left-right direction and includes an auger shaft whose both ends are rotatably supported by the both side walls of the second waste toner accommodating portion  45  (conveying chamber  91 ) and an auger blade formed around the auger shaft and helically extending in the left-right direction. 
     The waste toner accommodating chamber  92  is defined as a lower space of the second waste toner accommodating portion  45 , in which waste toner (e.g., transfer residual toner) collected by the cleaning roller  42  is stored. 
     As illustrated in  FIG. 3 , a plurality of paper feeding ribs  97  each formed into substantially a triangular shape as viewed from a side are vertically provided on the front surface of the second waste toner accommodating portion  45  that faces the paper guide section  46  (described later). The paper feeding ribs  97  are arranged spaced apart from each other in the left-right direction. The front end surface of each paper feeding rib  97  extends substantially in the up-down direction. 
     (3-3) Connection Portion 
     The connection portion  81  connects the left ends of the first waste toner accommodating portion  44  and the second waste toner accommodating portion  45 . The front end of the connection portion  81  is opposed to the left side of the first waste toner accommodating portion  44  from left to right. The rear end of the connection portion  81  is opposed to the left side of the second waste toner accommodating portion  45  from left to right. A connection/conveying chamber  98  formed into substantially an ellipsoidal shape extending from the front side lower end of the connection portion  81  to rear side upper end is defined in the connection portion  81 . 
     The front end of the connection/conveying chamber  98  is opposed to the first conveying auger  87  of the first waste toner accommodating portion  44  in the left-right direction and communicates with the inside of the first waste toner accommodating portion  44  at the opposing portion. 
     The rear end of the connection/conveying chamber  98  is opposed to the second conveying auger  95  of the second waste toner accommodating portion  45  in the left-right direction and communicates with the inside (conveying chamber  91 ) of the second waste toner accommodating portion  45  at the opposing portion. 
     The connection/conveying chamber  98  includes a belt conveying section  101  (an example of a first conveying member). 
     The belt conveying section  101  includes a driving pulley  102 , a driven pulley  103 , and a conveying belt  104 . The driving pulley  102  is disposed at the lower side of the front end of the connection/conveying chamber  98 . The driven pulley  103  is disposed at the upper side of the rear end of the connection/conveying chamber  98 . The conveying belt  104  is spanned between the driving pulley  102  and the driven pulley  103 . 
     An engagement plate  99  is provided between the right ends of the first waste toner accommodating portion  44  and the second waste toner accommodating portion  45  as illustrated in  FIG. 2 . The engagement plate  99  is formed into substantially a rectangular shape as viewed from a side and abuts against the rear end surface of the first waste toner accommodating portion  44  and the front end surface of the second waste toner accommodating portion  45 . As a result, the right ends of the first waste toner accommodating portion  44  and the second waste toner accommodating portion  45  are relatively positioned spaced apart from each other in the front-rear direction. 
     The upper end of the engagement plate  99  is integrally formed with the right side second flange portion  59  so as to be held by the right side second side plate  56  of the drum frame  51 . 
     (3-4) Paper Guide Section 
     The paper guide section  46  is formed as an opening. The paper guide section  46  penetrates the cleaning unit  41  in the up-down direction at the front-rear midway portion of the cleaning unit  41 . More specifically, the paper guide section  46  is defined by the first waste toner accommodating portion  44 , the second waste toner accommodating portion  45 , the connection portion  81 , and the engagement plate  99 . The left-right direction width of the paper guide section  46 , that is, a distance between the connection portion  81  and the engagement plate  99  is set larger than the width of the paper sheet P. 
     (3-5) Movement of Paper Sheet Passing Through Paper Guide Section 
     As described above, the paper sheet P that has passed through the opposing portion between the intermediate transfer belt  22  and the secondary transfer roller  24  is guided by the paper guide section  46  to pass through the cleaning unit  41  in the up-down direction toward the fixing unit  17 . 
     At this time, the leading end (downstream side end in the feeding direction) of the paper sheet P is moved upward while abutting against the front end surfaces of the paper feeding ribs  97  provided on the front end surface of the second waste toner accommodating portion  45 . As a result, the paper sheet P is smoothly guided toward the fixing unit  17  along the front end surfaces of the paper feeding ribs  97 . 
     (4) Cleaning Operation 
     As described above, after the color image has been secondary-transferred onto the paper sheet P, the transfer residual toner (waste toner) remains on the peripheral surface of the intermediate transfer belt  22 . When the waste toner has reached to a position opposite to the cleaning roller  42  with the circulation of the intermediate transfer belt  22 , the waste toner is moved from the intermediate transfer belt  22  to the peripheral surface of the cleaning roller  42 . As a result, the waste toner is removed from the peripheral surface of the intermediate transfer belt  22 . 
     Thereafter, with a rotation of the cleaning roller  42 , the waste toner carried by the peripheral surface of the cleaning roller  42  reaches a position opposite to the metal roller  85  and then moves from the peripheral surface of the cleaning roller  42  to the peripheral surface of the metal roller  85  to be adhered thereto. 
     Then, when the metal roller  85  rotates, the waste toner adhered to the peripheral surface of the metal roller  85  is scraped by the scraping member  86  and dropped in the first waste toner accommodating portion  44 . 
     Thereafter, the waste toner that has dropped in the first waste toner accommodating portion  44  is conveyed leftward inside the first waste toner accommodating portion  44  by a rotation of the first conveying auger  87  to be conveyed from the first waste toner accommodating portion  44  to the connection/conveying chamber  98 . 
     The waste toner that has been conveyed to the connection/conveying chamber  98  is conveyed in the upper-rear direction by the belt conveying section  101  and is thereafter conveyed from the rear side upper end of the belt conveying section  101  to the conveying chamber  91  of the second waste toner accommodating portion  45 . 
     The waste toner that has been conveyed to the conveying chamber  91  is conveyed rightward by a rotation of the second conveying auger  95  and is dropped in the waste toner accommodating chamber  92  through the communication port  94  formed in the partition  93 . In such a manner, the waste toner is stored in the waste toner accommodating chamber  92 . 
     3. Attachment of Developer Cartridge to Drum Unit 
     As illustrated in  FIG. 5 , attachment of the developer cartridge  31  to the drum unit  15  is performed in a state where the drum unit  15  is positioned at the pull-out position at which the drum unit  15  is outside the main casing  2 . 
     At this time, the front cover  5  is positioned at an opening position at which the upper end (free-end portion) is separated from the main casing  2  and inclined frontward. 
     First, the developer cartridge  31  is disposed above the drum unit  15 . In this state, the developing roller  36  is positioned at the relatively lower side and the toner accommodating portion  39  is positioned at the relatively upper side. 
     Then, the developer cartridge  31  is moved downward. As a result, the developer cartridge  31  goes between both the first side plates  55  of the drum frame  51 . When the developer cartridge  31  is moved further downward, the peripheral surface of the developing roller  36  abuts against the peripheral surface of the corresponding photosensitive drum  32 . In this state, further downward movement of the developer cartridge  31  is restricted by a restricting portion (not illustrated) provided in each first side plate  55  to thereby complete the attachment of the developer cartridge  31  to the drum unit  15 . 
     After the completion of the housing operation of the developer cartridge  31  in the drum unit  15 , the drum unit  15  is moved from the pull-out position to the housing position. 
     As illustrated in  FIGS. 5 and 6 , when the drum unit  15  is moved to the housing position, the handle portion  61  of the drum unit  15  is grasped to move the drum unit  15  rearward. As a result, the first and second flange portions  57  and  59  are guided rearward along a rail member (not illustrated) formed in the main casing  2 . 
     Afterward, further rearward movement of the drum unit  15  brings a roller member (not illustrated) provided at the rear end of the rail member into contact with the first and second inclined surfaces  58  and  60  to cause the entire drum unit  15  to move to the lower rear side along the first and second inclined surfaces  58  and  60 . Then, each photosensitive drum  32  abuts against the peripheral surface of the intermediate transfer belt  22  to restrict the further rearward and downward movement of the drum unit  15  to complete the movement of the drum unit  15  to the housing position in the main casing  2 . 
     The pull-out operation of the drum unit  15  outside the main casing  2  can be performed in the reverse order to the order of the above procedure. 
     4. Functions/Effects 
     As described above, the cleaning unit  41  is disposed above the intermediate transfer belt  22  and includes the cleaning roller  42  and the casing  43  that supports the cleaning roller  42 . The cleaning roller  42  is disposed downstream of the secondary transfer roller  24  and on the upstream side of the upstream most photosensitive drum  32  in the travel direction of the intermediate transfer belt  22 . The cleaning roller  42  is brought into contact with the intermediate transfer belt  22  to collect the waste toner remaining on the intermediate transfer belt  22  that has passed through the secondary transfer roller  24 . The paper guide section  46  is formed in a midway portion of the casing  43  in the front-rear direction, and the conveying path  8  passes through the paper guide section  46 . With this configuration, the size reduction of the color printer  1  can be achieved while ensuring the capacity of the casing  43  (cleaning unit  41 ). 
     Further, the paper guide section  46  is configured to guide the paper sheet P passing between the intermediate transfer belt  22  and the secondary transfer roller  24  toward the fixing unit  17  disposed above the cleaning unit  41 . With this configuration, the paper sheet P can be conveyed to the fixing unit  17  smoothly. 
     Further, the paper guide section  46  is formed as the opening portion defined by the first waste toner accommodating portion  44 , the second waste toner accommodating portion  45 , the connection portion  81 , and the engagement plate  99 . With this configuration, the mechanical strength of the casing  43  can be secured. As a result, the paper sheet P can be guided while ensuring the mechanical strength of the casing  43 . 
     The casing  43  includes the second waste toner accommodating portion  45  for accommodating the waste toner. The second waste toner accommodating portion  45  is provided on the opposite side (rear side) of the cleaning roller  42  with respect to the paper guide section  46 . There is no restriction as to arrangement of members for feeding operation of the paper sheet P in a region on the rear side of the cleaning roller  42  with respect to the paper guide section  46 . Thus, a sufficient size can be ensured for the second waste toner accommodating portion  45 . 
     The cleaning unit  41  includes the first conveying auger  87  and the belt conveying section  101  that convey the waste toner collected by the cleaning roller  42  toward the second waste toner accommodating portion  45 . With this configuration, the waste toner can smoothly be conveyed to the second waste toner accommodating portion  45 . 
     The first conveying auger  87  conveys leftward the waste toner collected by the cleaning roller  42 . The belt conveying section  101  is provided on the left side of the casing  43  and conveys the waste toner that has been conveyed to the first conveying auger  87  to the second waste toner accommodating portion  45 . As a result, the waste toner can efficiently be conveyed to the second waste toner accommodating portion  45 . 
     When being projected in the opposing direction between the photosensitive drum  32  and the intermediate transfer belt  22  (i.e., up-down direction), the fixing unit  17  and the cleaning unit  41  are disposed so as to at least partially overlap each other. As a result, a distance between the fixing unit  17  and the cleaning unit  41  can be reduced. Further, the front-rear direction size can be reduced as compared to a configuration in which the fixing unit  17  and the cleaning unit  41  are disposed so as not to overlap each other when being projected in the up-down direction, with the result that the size of the color printer  1  can be reduced further. 
     The color printer  1  includes the drum unit  15  that integrally retains the photosensitive drums  32  and the cleaning unit  41 . The drum unit  15  is provided so as to be movable between the housing position at which the drum unit  15  is housed in the main casing  2  and the pull-out position at which the drum unit  15  is outside the main casing  2 . With the above configuration, moving the drum unit  15  to the pull-out position allows the cleaning unit  41  and the photosensitive drums  32  to be pulled out integrally outside the main casing  2 , making it easy to perform replacement and maintenance works for the cleaning unit  41 . 
     &lt;Second Embodiment&gt; 
     In the color printer  1  illustrated in  FIG. 1 , the cleaning unit  41  is provided in the drum unit  15 , and the drum unit  15  is attached/detached to/from the main casing  2 . 
     Alternatively, in the present embodiment, as illustrated in  FIGS. 7 and 8 , the cleaning unit  41  is directly attached/detached to/from the main casing  2  without providing the drum unit  15 . 
     In a color printer  151  illustrated in  FIGS. 7 and 8 , a main body side opening portion  152  (an example of a main casing side opening) for communicating between the inside and outside of the main casing  2  is formed in the front side wall of the main casing  2 . Further, a front cover  153  capable of opening/closing the main body side opening portion  152  is formed on the front side wall of the main casing  2 . 
     The main body side opening portion  152  has an up-down direction width and a left-right direction width allowing passage of the cleaning unit  41 . 
     Thus, opening the front cover  153  to open the main body side opening portion  152  allows the cleaning unit  41  to be pulled out frontward through the main body side opening portion  152 . This configuration allows the cleaning unit  41  to be attached/detached to/from the main casing  2 . 
     An upper side opening portion  156  is formed in the upper wall of main casing  2 . Further, a top cover  157  capable of opening/closing the upper side opening portion  156  is provided in the main casing  2 . 
     Four LED units  155  are supported at the inner surface (lower surface) of the top cover  157  so as to move following a pivotal movement of the top cover  157 . 
     When the top cover  157  is opened, the four LED units  155  move upward in conjunction with the pivotal movement of the top cover  157 . As a result, the four LED units  155  escape from the main casing  2 . 
     Four process cartridges  158  corresponding respectively to the four LED units  155  are arranged in the main casing  2 , spaced apart from each other in the front-rear direction. Each process cartridge  158  retains the photosensitive drum  32  and the developing roller  36 . 
     After the four LED units  155  have escaped from the main casing  2  with the opening of the top cover  157 , the process cartridges  158  can be attached/detached to/from the main casing  2  through the upper side opening portion  156 . 
     Even in such a configuration, the same effects as in the first embodiment can be obtained. 
     &lt;Other Embodiments&gt; 
     Although the first and second embodiments of the present invention have been described as above, the present invention may be practiced in other embodiments. 
     For example, in the above embodiments, the paper guide section  46  is formed as the opening portion defined by the first waste toner accommodating portion  44 , second waste toner accommodating portion  45 , connection portion  81 , and the engagement plate  99 . 
     However, the paper guide section  46  may be formed by a region inside substantially a U-like shape as viewed from above opened leftward or rightward. Even in a color printer adopting such a paper guide section  46 , the same effects as in the color printer  1  of  FIG. 1  can be obtained.
An image forming device includes: a photosensitive drum; a first roller; a second roller; an intermediate transfer belt; a transfer roller; a cleaner; a waste toner accommodating portion; and a paper guide. The intermediate transfer belt is looped around the first roller and the second roller to circularly move in a moving direction. The intermediate transfer belt contacts the photosensitive drum. The transfer roller is disposed opposite to the first roller with respect to the intermediate transfer belt. The cleaner collects waste toner on the intermediate transfer belt. The cleaner is disposed upstream of the photosensitive drum in the moving direction and downstream of the transfer roller in the moving direction. The waste toner accommodating portion accommodates the waste toner collected by the cleaner. The paper guide guides a recording medium and disposed between the cleaner and the waste toner accommodating portion.