PURPOSE: To obtain the driving method of a print head, in which the length of a dot is not changed even when a time is changed, by a method wherein a plurality of times of basic printing process and correcting printing process are repeated in the printing of one dot.

CONSTITUTION: In AND gates 28a-28d, the ANDs of MSBs of printing data of corresponding dots and the correcting data of corresponding dots are read out. Upon reading of the printing data of a third time and the reading of the correcting data of a second time, the third bits of the correcting data is read out, upon the reading of the printing data of a fifth time, the data of LSB of correcting data are read out. The printing data, corresponding to respective data, and data, processed through AND process, are supplied to a LED driving circuit. Thereafter, the cycle of the basic printing, four times of correcting printings and the basic printing, is repeated four times.