Under a condition in which bowed printing occurs, a horizontal shift is suppressed to improve print quality. Following a program stored in a ROM 12, an MPU 10 generates video data for charging print particles according to print contents data stored in a RAM 11 . Based on the print contents data, the MPU 10 detects a letter to be printed last, and when the letter to be printed last is printed to end a print operation, generates video data so that based on the video data, a non-print charge voltage driving non-print particles to an extent that they do not fly over a gutter 25 is applied to non-print particles. The number of the non-print particles subjected to the non-print charge voltage is determined by the MPU 10, based on the distance from a print head 2 to a print subject 30, a letter height preset value, etc. A character signal generating circuit 18 generates the non-print charge voltage, based on the video data, and applies the generated the non-print charge voltage to a charging electrode 22.