PURPOSE: To obtain an image rotated a previously decided angle from images stored in a page memory in a short time.

CONSTITUTION: Image data supplied from an image data supplying part 1 of a computer or the like are extended in a page memory 3 by an MPU 6. When extending the image data in this page memory 3, a write area judging part 10 judges an extended area. Partial rotation processing is executed to the judged area and stored in the page memory 3 again. Further, when supplying pixels from the page memory 3 to an n×n pixel rotating part 5 (n) by (n), an n×n white picture element judging part and an n×n black pixel judging part respectively detect small blocks to stop the partial rotation processing. Since unwanted partial rotation processing is not performed, the rotated image can be obtained in a short time.