PURPOSE: To prevent the shift of the line feed pitch of printing paper by providing a carriage loaded with a printing head and reciprocally moving in a horizontal direction with respect to the printing paper and a control means for moving the carriage to the center of the printing paper at the time of the line feed of the printing paper based on the detection result of a detection means for detecting the width of the printing paper.

CONSTITUTION: With respect to printing paper 19 having a width of B, the width of the printing paper 19 is detected on the basis of the detection signals from detection sensors 20a, 20b by a paper width detection part 30. When one line is printed by a printing head 13, a printer control part 22 moves the printing head 13 to the center of the printing paper 19 on the basis of the paper width detection part 30. Thereafter, the line feed of the printing paper 19 is performed. The printer control part 22 moves the printing head 13 positioned at the center of the printing paper in a direction wherein the moving distance of a printing start position is shorter among the moving distances to the respective left and right of the printing data of one line, to print the printing data of one line. When the printing of one page is finished, the printing paper 19 is discharged to a predetermined position.