After document data have been inputted by operating character keys, if an automatic setting key is operated to allow the print character size to be set automatically and a print key is then operated, printing process control is executed and the greatest character size printable on a tape mounted in the tape printing apparatus is set (S33), a base line position shifting process is performed so that the character is positioned around the center of the width of the tape (S34). Then, dot image data in the print character size that is set on the basis of the document data is generated (S31) and the dot image data is output to the printing mechanism to be printed on the tape (S32).