PURPOSE: To transmit image data to be printed by a printing apparatus to a host computer so that the image data correspond to printing data.

CONSTITUTION: A processor 3 receives an editing instruction signal together with a readout instruction signal from a host computer 3 and gives readout and editing instructions to a compression and extension circuit 7, image contraction and expansion circuit 8 and page memory 9. The page memory 9 outputs image data stored on the basis of the editing instruction signal to the compression and extension circuit 7 or image contraction and expansion circuit 8. The image data outputted to the compression and extension circuit 7 and image contraction and expansion circuit 8 are edited on the basis of the editing instruction signal. The image data edited on the basis of the editing instruction signal are sent out to the host computer 1 via the processor 3.