PURPOSE: To reduce the storage information volume per one image by compressing the image only in an area designated by a compression area designating part to store the compressed image in an image storage part.

CONSTITUTION: When a document is inputted from an image input device 15 at the time of registering the document, a control part 14 reads in a compression area part 17 to obtain position information of the compression area and reports it to a compressing/expanding part 13. The compressing/expanding part 13 compresses the image only in the area designated based on this position information, and the compressed image is written in an image storage part 19 by the control part 14. At the time of retrieval, the compressed image in the image storage part 19 is read out by the control part 14 and is expanded by the compressing/expanding part 13 and is developed in an image synthesizing part 12. The control part 14 reads out the guide image of a form and expands it by the compressing/expanding part 13 and develops it in the image synthesizing part 12 to synthesize it with the preliminarily developed image. Thus, the document volume stored in the storage part is increased.