To judge the paper feeding irregularity in an ink-jet printer easily by the visual observation.

In an on-demand type color ink-jet printer, different colors K, MCY are printed by a dot lint repeatedly with a constant cycle while feeding by the minimum resolution of the printer. In the method for detecting the paper feeding irregularity of an ink-jet printer, the length of printing is not shorter than the developed length of one rotation of a paper feeding roller, a paper feeding motor, and a gear transmitting the rotation of the paper feeding motor to the paper feeding roller, and only one nozzle of each head is used as the nozzle of the head for printing the different colors. According to the method, judgment can be made only by the visual observation instead of the conventional method of measuring the length. Moreover, by measuring the pitch of the irregularity, the cause thereof can be specified.