PURPOSE: To make sure that the load of CPU is reduced and the processing speed of a form overlay action is accelerated by extending form data equal to a compressed single line and writing the extended form data in memory and outputting character image data which is ORed with form data during form overlay action.

CONSTITUTION: A page printer device outputs form data developed in bit map memory MB 86 which is ORed with character image data to a printing device 90. In this case, a means AEL 89 for converting compressed image data to intermediate data which represents the length and black/white of a dot image and further converting the intermediate data to form data is provided on said device. In addition, during form overlay action, the AEL 89 is allowed to perform the process to convert the compressed image data to the intermediate data and the process to expand the intermediate data and write the form data in the BM 86 for each single page repeatedly. In addition, character image data prepared in parallel in the CPU 81 is ORed with the formed data using BM 86 and the ORed data is output using a printing device 90.