PURPOSE: To save the output time or an output medium by providing a means discriminating whether the calculated value of an operation means coincides with the value stored in a memory means and a means outputting only a page image wherein a discrimination result becomes non-coincidence.

CONSTITUTION: When the image data of a first page is written in a frame buffer, the image data is transmitted to a video interface 9 from an RAM 3 by a DMA controller 8 and converted to a printable form to be supplied to a printer engine 11. A CPU 1 issues a printing start command to a controller 10 to start the printer engine 11 to print the image of the first page. The calculated value of each page image is compared with the past calculated value to judge whether the page image is altered with respect to the past printing page and only an altered page is printed. Therefore, a time printing a page not corrected when a corrected document is reprinted and paper can be conserved.