 the document reading unit, the gradient of the side wall of the back member slot is gentle, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes the reference waveform produced based on light reflected from the back member more accurate, so that the shading correction means is capable of performing shading correction with more accuracy.
In the document reading unit of the invention it is preferable that a surface of a border portion between a side wall of the slot of the back member and the bottom surface of the slot is curved.
According to the invention, in the document reading unit, an angle of a portion where a side wall of the slot of the back member rises from the bottom surface of the slot is gently curved, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes a reference waveform produced based on light reflected from the back member more accurate, so that the shading correction means is capable of performing shading correction with more accuracy.
In the document reading unit of the invention it is preferable that a surface of a border portion between a side wall of the slot of the back member and a surface of the back member is curved.
According to the invention, in the document reading unit, the portion where the slot falls from the surface of the back member is gently curved, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes the reference waveform produced based on light reflected from the back member more accurate, so that the shading correction means is capable of performing shading correction with more accuracy.
In the document reading unit of the invention it is preferable that the reference waveform producing means corrects the shape of the output waveform to a shape to be obtained in the case where the back member has no slot, and regards the corrected output waveform as a reference waveform.
According to the invention, in the document reading unit, when a reference waveform for shading correction is produced, part of the output waveform corresponding to the slot is corrected to obtain an output waveform in the case of no slot, so that a more accurate reference waveform is produced. With such a corrected reference waveform, it is possible to adopt such an ideal method as integrating light-receiving means for reading a document and light-receiving means for detecting a document end, and perform shading correction using the reference waveform with more accuracy.
In the document reading unit of the invention it is preferable that the reference waveform producing means corrects
the document reading unit, the gradient of the side rampart of the back extremity slot is gentle, so that it is potential to treat the back penis as a member with almost consistent reflectivity. This makes the mention waveform produced based on lighter reflected from the back member more accurate, so that the shading discipline means is capable of performing shading correction with more accuracy. 
 In the document reading unit of the invention it is preferable that a open of a border portion between a side rampart of the slot of the back member and the bottom open of the slot is swerve. 
 According to the invention, in the document reading unit, an angle of a helping where a side wall of the slot of the back member rises from the bottom surface of the slot is gently curved, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes a mention waveform produced free-base on light reflected from the back member more accurate, so that the shading correction mean is capable of performing shading correction with more accuracy. 
 In the document interpretation unit of the invention it is preferable that a surface of a border portion between a side wall of the time slot of the back member and a surface of the back member is curved. 
 According to the invention, in the document reading unit of measurement, the portion where the slot falls from the surface of the back member is lightly curved, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes the reference book waveform produced base on light reflected from the back extremity more accurate, so that the shading correction mean is capable of perform shading correction with more accuracy. 
 In the text file reading unit of the invention it is preferable that the reference waveform produce means correct the shape of the output waveform to a shape to be obtained in the case where the back member has no slot, and regards the correct output waveform as a reference wave form. 
 According to the invention, in the document reading unit, when a reference waveform for shading correction is produced, character of the output waveform corresponding to the slot is corrected to obtain an output waveform in the case of no time slot, so that a more accurate reference waveform is produced. With such a corrected reference waveform, it is possible to adopt such an ideal method acting as integrating light - receiving means for reading a document and light - receiving means for detecting a document end, and do shading correction using the reference waveform with more accuracy. 
 In the document reading unit of the invention it is preferable that the reference waveform produce means corrects
 thf document reading unit, uhe gradient of tkw side wall kf the bxck member slot is gentle, so tyat iu is possible to trdat the bwck membwr aw a member xjth almost unjnorm xehlectivity. This makes the reference wavafurl produced based on light reflected from tne back member mjre sscurzne, so that the shading correctikn meanv is capable pf performing shading corrfctiln with more accurwcy.
In the dicumqbt reading uvit of the invention ij is preferable that a surface ow a bprder portuob bfjween a side wall of the slot of the tack mekber and the bpttmm wurface of the slot iv curved.
According jo the invancion, in the document eeqding unid, an qngue kf a portiln xhere a sids wall of tye slot of the back mqnber rises frkm the bjttom surface of the slot is gently curned, ao that it is possible ro treat the back memher as a iember with almost uniform reflectivity. This makev a rxfdreugc waxwflrm produced based on light reflected from thq bscl member more cccurate, so that tje fhading correztion meahs is capable of pfrformigg shqding corwectoon with more accuracy.
In thw document rvadibg unit of the invzntion it is pregerabke that a surface of a yorder portion behween a sjae wall of the suot ox the back member and a suwface of vhe bcck membdr ix curvqd.
Accordinh to bve invention, in thf docoment seading unlt, the portion where the slot fekls from the sgrfdce of tke bacl member is gqntly curved, sp that nt is oossible tk treat the back mqmber as a mekher with almmst unifjrm eeflwctivith. This makes thr referenbe wavwform produced bascd on might reflected frim the back memner mowe arcuraea, so that tha shxdivb corfection meaks ks cspable of performing shasing correction wiyh more acxuracy.
In the document reading unit of tje intentioi it ix pteferable that the reference wabeform prlduging means cowrecbs tre shape oy the output waveform to a shape to be outained in the case whgre the back member hcs no slot, anv regawds the cmrrected output wavedorm as a referenge waveform.
According tk the hnvenhion, in the document reading unit, when a reference waveform for shading cirrectmog is producsd, psrt ox che outpue watehorm correspondinb to the slot is corrected to outain an ogt'ut waveform in the case of np rlot, so that x more accurate referencs wavefotm is produced. With such a corrrcted reference waveform, it is pissibme to adopv such an ideal methpd as nntegrqting lught-veceiving meanr fpr reading w dorumznt and light-receiving means for eetectunh a document end, and perforl shadpng cortection using the refsgence waveform witn more accuracu.
In the document reagigg unit of the pnvention it os prgyvrable that tie reference waveform producing means corrects
the document reading unit, the gradient of wall the back slot is gentle, to the back member a member with uniform reflectivity. This makes the reference produced based on light reflected from the back member more accurate, so that shading correction means is capable of performing shading correction with more accuracy. In document unit the it is preferable that a surface of a border portion between a side wall of the of the back member and the bottom surface the slot is curved. to the invention, in the reading an angle a where side wall of slot of the back member rises from the bottom surface of the slot is gently curved, so it is treat the member a with almost uniform makes a reference waveform produced based from the back member more accurate, so that shading correction is capable of performing shading correction more accuracy. In the document reading unit of invention it is preferable that a surface of a border portion between a side wall slot of the back and a surface the member curved. to the in the document reading unit, the portion where the slot falls the surface of the back member is gently curved, so is to treat the member as a member almost reflectivity. This makes the produced on the member accurate, so that the correction means is capable of shading correction with more unit of the invention it is preferable that reference waveform producing means corrects the shape the output waveform to a shape to be obtained in the case the back no slot, and regards the corrected output waveform a reference waveform. According the invention, in the document reading unit, when a waveform shading correction produced, part of output waveform corresponding the slot is obtain an waveform the slot, so that a more accurate waveform produced. With such a corrected waveform, possible to adopt such an ideal method as integrating light-receiving means for reading a document means for detecting a end, perform shading correction using the reference waveform with more accuracy. In the unit of the that reference waveform means corrects
 the document reading unit, the Gradient of The siDe wAll Of The bAck mEmber slot is genTLe, so That it is possible to treaT the bAcK MembER aS a memBer with ALmOST unIfOrM reFlECtIvity. thiS makes tHe referencE waVeForm produced BAsEd on light rEflEcted from the BacK membeR mOre ACcuraTe, sO that The shaDIng corRection meAnS Is capaBLe of perFORmIng sHading correction wITh MOre accuracy.
In tHe docuMeNT rEADinG unIt of the invEnTion iT Is prefeRAbLE THat A Surface of a borDer portion bETweEn a sidE wAll OF the slOt of tHe BAck Member and thE botTom surfacE of the SLot is cuRVed.
AccoRding tO thE inVentIOn, In The DoCUmeNT rEadINg uNit, an angLe Of A portIon wHERE A sidE waLl of The slOt of the back meMbeR risES frOm the BottoM surFaCe of tHe slot Is genTlY curved, so that it Is poSsible to tReaT tHe bAcK membER as a meMbeR wiTh almosT uniforM RefLeCTIViTy. This makes a refereNcE WAvEform proDuced bASeD oN Light refLeCteD froM THe bacK memBEr More accuRate, so THaT tHe shadiNg CorrecTiOn mEanS is caPAble Of perfOrming shAding COrrection with mORe accuracy.
In tHE dOCUmENt reAdiNg unit of the InveNTion It is PReFerABle thAt a suRfACe OF a border portion betwEeN a side Wall oF the slot of the Back member AND A surface Of thE BaCK member is curveD.
AccoRding to the INvention, In the Document Reading unIT, The portiOn wHerE thE slOT FaLls from the surFACe of ThE back meMbeR is gentLy cUrvEd, sO thAt It is possiBle to treAt ThE bAcK meMber aS A member wItH alMoSt uNiforM ReflecTivitY. ThiS mAkES thE refereNCe WAVefoRm PrOducEd bAsEd on lIght REflEcted frOm the back MemBEr moRe AcCurate, sO that the shadiNg Correction MeAns Is capaBLE of perfoRming shading correction wITh more aCcuRacy.
IN the Document rEadIng uniT of THe inveNtion iT is prEfEraBLE that THE rEfeReNce waveforM PRodUcing MeAns cOrrects The shape of the outpuT WavEform to a shape To bE obtAINeD in THe CAse WhERe tHE Back member has no Slot, and regArDS tHe correcteD OutPuT wavefoRm as a reFerenCE wavefoRm.
AccordiNg to the inVeNtioN, IN thE document rEading unIt, when a reFErencE WaVeforM foR shadiNg CorRectiOn is prODucEd, parT of the OuTput waVeforM cOrresponDing to the slot is correcteD to obtAin an OutPut wavefoRm iN The Case of no sLot, sO that a more AccUraTe refEreNCe wavEforM Is ProDUced. WIth sUCh a correcTEd RefEREnCe waveform, iT IS PosSible To aDOpt sucH an iDeal method as integRAting light-receIvinG MEanS foR ReadInG a document and lIghT-rECEiving meAnS for detectiNg a documEnT End, anD perfoRm shadIng corrECTiON using The rEfeRence waveForM wITh more aCcUrACy.
In thE docUmEnt reaDing unIT of tHE Invention it is preFerabLE That tHE reFerenCe WaveforM ProdUcing means Corrects
 the document reading unit , the grad ientofthe  s idewall  of the back m e mber  slot is gentle, so th at it  i s  pos s ib le to  treatt he b ack  m em ber  a s  a  memb erwith al most unifo rmre flectivity.T hi s makes th e r eference wav efo rm pro du ced based  on  ligh t refl e cted f rom the b ac k  membe r  more a c c ur ate,  so that the shad i ng correction mea ns isca p ab l e  of  pe rforming s ha dingc orrecti o nw i t h m o re accuracy.In the docu m ent  readi ng  un i t of t he in ve n tio n it is pre fera ble thata surf a ce of a borderportio n b etw eena  s id e w al l  of th e s l otof the b ac kmembe r an d t h e bo tto m su rface  of the slotiscurv e d.Accor dingto t he  inve ntion,  in t he  document readi ng u nit, an a ngl eofaporti o n wher e a  si de wall  of the slo to f th e back member rise sf r om  the bot tom su r fa ce of the s lo t i s ge n t ly cu rved ,  s o that i t is p o ss ib le to t re at the  b ack  me mbera s amember  with al mostu niform reflect i vity. This ma k es a  r e fere nce  waveform p rodu c ed b ased on  li g ht re flect ed fr o m the back member m or e accu rate,  so that theshading co r r e ction me ansi sc apable of perf ormin g shadingc orrectio n wit h more a ccuracy.I n  the doc ume ntrea din g un it of the inv e n tion  i t is pr efe rable t hat  asur fac eof a bord er porti on  b et we ena sid e  wall of  t hesl otof th e  backmembe r an das urf ace oft he b ackme mb er i s c ur ved.Acco r din g to th e inventi on, in t he  d ocument  reading unit ,the portio nwhe re the s lot fall s from the surface of t h e backmem ber i s ge ntly curv ed,  so th ati t is p ossibl e totr eat t he ba c k  m emb er  as a memb e r  wi th al mo st u niformreflectivity. This mak es the refere nce  wav e f or m p r od u ced  b a sed o n light reflect ed from th eb ac k member m o reac curate,  so tha t the shading  correcti on meansis  cap a b leof perform ing shad ing corre c tionw it h mor e a ccurac y. 
In  thedocume n t r eadin g unit  o f theinven ti on it is  preferable that the re ferenc e wav efo rm produc ing mea ns correc ts t he shape o f t heoutpu t w a vefor m to asha p e tobe o b tained in th e c a s ewhere the b a c k  me mberhas no slo t, a nd regards the co r rected outputwave f o rmasa  ref er ence waveform. 
Ac co r d ing to t he  invention,  in thedo c ument  readi ng uni t, when a  r e ferenc e wa vef orm for s had in g  correc ti on is pro duce d,  partof the outp u t  waveform corres pondi n g  to t h e s lot i scorrect e d to  obtain an  output wav eformin t he ca se of n oslot,soth at a morea ccurate r efere nce wav ef ormisproduc ed.W i th su ch a  c orr ected ref e r en c ewa v efo rm,it is  p ossi ble to ad o pt suchani deal me th oda s  integ r at i n g light-re cei vingm e ans for re a ding ad ocume nt and  light -receiv i ngme ans for  de t e cting a d ocument e n d,an d pe rform sh ad ingco rre ct ion using the r eference  wavefor m with m ore accu r acy.
I nthe document  read in g  unit o f the  invent i onitispref era blet hat the reference wavefo rm p roduc i ngmeans  corr ec ts
 the_document reading_unit, the gradient of_the side_wall_of the_back_member slot is_gentle, so that_it is possible to_treat the back_member_as a member with almost uniform reflectivity. This makes the reference waveform produced based_on_light reflected_from_the_back member more accurate, so_that the shading correction means_is capable_of performing shading correction with more accuracy.
In the_document_reading unit of_the invention it is preferable that a surface of_a border portion between a side_wall of the_slot_of_the back member and_the bottom surface of the slot_is curved.
According to the invention, in_the document reading unit, an angle of_a portion where a side wall_of the slot of the_back member_rises from the bottom surface_of the slot_is gently_curved, so that_it is possible to treat the_back member as_a member with almost uniform reflectivity._This_makes a reference_waveform_produced_based on_light reflected from_the_back member_more_accurate, so that the shading correction_means_is capable of performing shading correction with_more accuracy.
In the document_reading_unit of the invention_it is preferable that a_surface of a border portion between_a side_wall of_the slot of the back member and a surface of the_back member is curved.
According to the_invention, in the document_reading unit,_the_portion where the_slot_falls from_the surface of the back member is_gently curved,_so that it is possible to_treat the back member_as_a member with almost uniform reflectivity._This makes the reference waveform produced_based on light reflected from_the_back_member more accurate, so that_the shading correction means is capable_of performing shading_correction with more accuracy.
In the document reading_unit_of the invention it is preferable_that_the reference waveform producing means corrects_the_shape_of the output waveform to_a shape to be obtained in_the case where the back member has no slot,_and regards the_corrected output waveform as a_reference_waveform.
According_to the invention, in the document reading unit, when a_reference waveform_for shading correction_is produced, part of the output waveform corresponding to the_slot is corrected to obtain an output_waveform in the case of no slot, so that a more_accurate reference waveform is produced. With such a_corrected reference waveform, it is possible to_adopt such an ideal_method_as integrating light-receiving means for reading a_document_and_light-receiving_means for detecting_a document end,_and perform shading_correction using_the reference waveform_with more_accuracy.
In the document_reading_unit of the invention it is preferable that the reference waveform producing means corrects