PURPOSE: To enable a high speed printing through parallel writing and reading of printing data, by dividing an image buffer memory for printing into longitudinal and lateral memory blocks respectively of equal capacities.

CONSTITUTION: An image buffer memory 1 for printing is constituted with longitudinal Yn dots and lateral Xn dots, and is divided into memory blocks of equal numbers longitudinally and laterally. In order for the printing portion 4 to print, a control portion 5 reads out printing data from the image buffer memory 1. The reading direction at the above time is indicated by Y, and firstly, memory blocks 0, 3 and 6 open, then 1, 4 and 7, open, and finally 2, 5 and 8 open to finish printing. Therefore, when the memory blocks 0, 3 and 6 are vacant, the following printing data are ready to be written into these blocks i.e. 0, 3 and 6.