8. A tape printing apparatus, comprising: print format-designating means for selecting one kind of print format as a designated print format, from a plurality of kinds of print formats, each print format corresponding to instructions initially stored in a memory; entry means for arranging entered characters to form a character string; print image-forming means for forming print image data by editing said character string based on the instructions for said designated print format; printing means for printing on a recording medium in the form of a tape being fed, based on said print image data, wherein said plurality of print formats are grouped into a first print format group including a vertical writing print format for printing, a horizontal writing print format for printing, and a second print format group including other print formats than said vertical writing print format and said horizontal writing print format, arranging means for making a lateral direction of said each character in agreement with a transverse direction transverse to a longitudinal direction of said recording medium in the form of a tape and arranging said each character in said longitudinal direction of said recording medium in the form of a tape for said vertical writing print format, and making a vertical direction of said each character of said character string in agreement with said transverse direction of said recording medium in the form of a tape and arranging said each character in said longitudinal direction of said recording medium in the form of a tape for said horizontal writing print format, wherein said second print format group includes a vertical writing index tab print format and a horizontal writing index tab print format for printing; and means for arranging said character string or said each character of said character string in a plurality of locations, said vertical writing index tab print format and said horizontal writing index tab print format each being used for making a label for an index tab, and wherein when any of said vertical writing index tab print format and said horizontal writing index tab print format is designated, said print image-forming means automatically sets a length of a printable area on said recording medium to a predetermined value suitable for said index tab, and forms said print image data by arranging character image data corresponding to said each character of said character string in an area corresponding to said printable area having said length thereof set to said predetermined value.
8. A tape printing apparatus, comprising: print format-designating means for selecting one kind of print format as a designated print format, from a plurality of kinds of print formats, each print format corresponding to instructions initially stored in a memory; entry means for arranging entered characters to form a character string; print image-forming means for forming print image data by editing said character string based on the instructions for said designated print format; printing means for printing on a recording medium in the form of a tape being fed, based on said print image data, wherein said plurality of print formats are grouped into a first print format group including a vertical writing print format for printing, a horizontal writing print format for printing, and a second print format group including other print formats than said vertical writing print format and said horizontal writing print format, arranging means for making a lateral direction of said each character in agreement with a transverse direction transverse to a longitudinal direction of said recording medium in the form of a tape and arranging said each character in said longitudinal direction of said recording medium in the form of a tape for said vertical writing print format, and making a vertical direction of said each character of said character string in agreement with said transverse direction of said recording medium in the form of a tape and arranging said each character in said longitudinal direction of said recording medium in the form of a tape for said horizontal writing print format, wherein said second print format group includes a vertical writing index tab print format and a horizontal writing index tab print format for printing; and means for arranging said character string or said each character of said character string in a plurality of locations, said vertical writing index tab print format and said horizontal writing index tab print format each being used for making a label for an index tab, and wherein when any of said vertical writing index tab print format and said horizontal writing index tab print format is designated, said print image-forming means automatically sets a length of a printable area on said recording medium to a predetermined value suitable for said index tab, and forms said print image data by arranging character image data corresponding to said each character of said character string in an area corresponding to said printable area having said length thereof set to said predetermined value. 10. A tape printing apparatus according to claim 8, wherein when said horizontal writing index tab print format is designated as said designated print format, said print image-forming means forms first horizontal writing character string image data by making a vertical direction of character image data corresponding to said each character of said character string in agreement with a direction corresponding to a transverse direction of said recording medium in the form of a tape and arranging said character image data in said direction corresponding to said longitudinal direction of said recording medium in the form of a tape, and second horizontal writing character string image data by arranging said character image data in a direction corresponding to a direction opposite to said longitudinal direction of said recording medium in the form of a tape such that said second character string image data is in an inverted position and in point symmetry with said first horizontal writing character string image data, and forms said print image data by arranging said first horizontal writing character string image data at a location corresponding to one side of a center line in said longitudinal direction of said recording medium in the form of a tape and said second horizontal writing character string image data at a location corresponding to another side of said center line in said longitudinal direction of said recording medium in the form of a tape.