PURPOSE: To enable a printing overlapping line without increase in the number of line/bit buffers by feeding back contents of the line/bit buffers to make a line overlapping data.

CONSTITUTION: A line overlapping stored in a line/bit buffer 7 to be controlled by a lead light signal 30, an address signal 15 and the like is fed back to an OR circuit 26 from the buffer 7. The data overlaps another overlapping data applied to the circuit 26 and is outputted via the buffer 7. The overlap printing requires no overlapping-specialized line/bit buffer to simplify the construction without increasing the number of line/bit buffers.