In an ink jet printer, a print head includes (N+1) nozzles arrayed in the paper feed direction. The distance between the adjacent nozzles is K times as long as the dot line pitch P. N and K are each an integer larger than 2, and mutually prime. The quantity of ink droplet discharged from each nozzle is adjusted so as to form on a print paper, dots each having the diameter at least 1.4 times as long as the dot line pitch. An interlaced print as the combination of a print of paths made by the N successive upper nozzles of the print head and a paper feed of N print line pitches is used for the print on the most part of the print paper. A minute-feed print as the combination of a print of paths made by the N successive upper or lower nozzles of the print head and a paper feed of one print line pitch is used for the print on the upper and lower end areas of the print paper that reject a perfect print by the interlaced print. With the combination of the interlaced print and the minute-feed print, a perfect print is made on the entire surface of the print paper.