PURPOSE: To ensure that processing time is fast and prevent image data from becoming lost when an abnormality occurs by erasing any appropriate image data stored in a storage device when a medium for image formation is ejected in a condition where a continuous image is formed with media for image formation.

CONSTITUTION: The subject device consists of a page buffer area 403a where image data sent from RAM 403 or a host device 409 is temporarily stored, an editted list area 403b and a sheet count area 403c. In the editted list area 403b, data on print position, the type, width and height of characters for image data of pages, for example, two pages and other necessary information for printing as well as an edited list of character codes are stored. The sheet count area 403c is set to 0 when a power supply is turned ON and 1 is added to its content, each time a print command is sent to an image control part 300. In addition, image data of a single page stored in the page buffer area 403a is printed on a sheet P in the engine control part 300. Then 1 is subtracted from the content each time the sheet P is ejected from the device.