Print is made on a recording paper by running an ink carriage along the supporting axis in a reciprocating motion. The ink carriage includes ink heads respectively provided with a front ink nozzle and a back ink nozzle facing their respective directions, so that print is made simultaneously at two portions on the recording paper along the transportation direction in which the recording paper is transported through a single transportation path one by one. Consequently, there can be provided an ink jet printer which can improve printing efficiency by increasing a printing rate and printing resolution, and realizing printing of an overstrike character, simultaneous printing of mixed information, double-side printing, etc.