Abstract: A compact-size and light-weight serial printer system for a desk-top calculator or a small electronic device. It uses an endless printing belt adapted to be circulated and carrying a number of printing fonts. A carriage on which the hammer mechanism provided is slidably mounted and a rack shaft are positioned within the inner side of the endless printing belt. A reference position detection means is provided to generate trigger signals, for detecting the reference position on the endless printing belt, for initiating printing operations, and for selecting a desired printing font in conjunction with processings by the control section to calculate a movement distance of the endless printing belt. A single driving source is provided to drive each mechanism of the printer system. On the endless printing belt, the fonts which have lower frequency of usage are included in a single section, and those fonts which have higher frequency of usage are included in several sections.