After an image compressed by a compressing portion is stored in a page memory, it is decoded by a decoding portion. A sub-scanning enlargement portion carries out sub-scanning direction enlargement processing upon the image decoded by the decoding portion and a printer prints out the enlarged image. At this time, the printer generates a printer synchronous signal each time when it scans an image formation object surface. A control portion provides the page memory, the decoding portion and the magnification changing portion with control signals so as to synchronize reading out of the image from the page memory, the decoding of the decoding portion and enlargement processing of the sub-scanning enlargement portion.