PURPOSE: To shorten a printing time by using a bit map memory in the bit developing processing of a next printing data block if there is space in the bit map memory used in developing processing on the basis of the number of the kinds of the data of a printing data block.

CONSTITUTION: For example, when a bit map memory use signal for an image and a bit map memory unuse signal for a figure and a character are applied to a mapping control circuit 23 on the basis of the confirmation code of the n-th page, signals SG1, SC1 making bit map memories 26b, 26c for a figure and a character usable in image development are formed and processed on the basis of an MPX output truth value table to determine the development data written in bit map memories 26a, 26b, 26c for an image, a figure and a character. The signals SG1, SC1 are processed according to the MPX output truth value table by an address selection circuit 25 to obtain the development data allotted to the bit map memories 26a, 26b, 26c. These addresses are set to predetermined preferential order to use other bit map memories in the developing processing of the image data of the next page.