To prepare an enlarged image of high quality by enlarging a multi- valued image by an enlarging method suited to the both for an edge part and a non-edge part and compositing the enlarged images.

An edge part image enlarging part 12 enlarges an image by using an enlarging method prepared for edge parts. A non-edge image enlarging part 13 enlarges an image by using an enlarging method prepared for non-edge parts. An area judging image preparation part 14 prepares an area judging image for judging whether or not it is an edge area by using images enlarged for the edge part and the non-edge part. An area judging part 15 judges whether a noticed area is an edge part or not by using the image prepared in the preparing part 14. An image compositing part 16 composites images based on the result judged by the area judging part 15.