A plurality of driver modules for energizing selected electrodes are mounted on a printing head. The printing head has 64 driver modules, each driver module connected to corresponding electrodes included in respective groups. Specifically, driver module No.1 is connected to electrode No.1 in group 1, electrode No.1 in group 2, ..., and electrode No.1 in group 32. Driver module No.2 is connected to electrode No.2 in group 1, electrode No.2 in group 2, ..., and electrode No.2 in group 32. During operation, at a time t1, each driver module sends a signal to a conductor connected to an associated electrode therewith in group 1. Then, at times t2, t3, ..., each driver module operates as above with respect to groups 2, 3, ..., sequentially. Meanwhile, when the pixel density values in a single group are partially different each other, a correction is performed.