PURPOSE: To secure orderliness of printed images in a column direction and contrive higher printing quality, by detecting the presence of an image printed in the preceding line in the same column as that of an image to be printed in the current printing line, and perform printing based on a detection signal.

CONSTITUTION: After reverse printing in a line (A) on a printing paper 3, the paper 3 is fed upward by a one-line amount by rotating a platen roll by a paper-feeding stepping motor. Next, forward printing is performed in a line (B). At this time, a detecting surface of a photoelectric element 8 is opposed to the line (A) to detect a printed part in the line (A). Based on a detection signal, an impact signal is outputted to a printing head 1, thereby printing in the line (B). Therefore, even when a carriage 4 is vibrated by some external action and it is not fed at a fixed velocity, printing positions in forward printing and those in reverse printing accord with each other in a column direction. Accordingly, orderliness of printed images in the column direction can be secured.