To decrease the data amount of medical images and to reduce the storage capacity of a storage device for storing the medical images by storing the image of difference between an image picked up after the second time and an image picked up for the first time in the storage device concerning that image picked up after the second time.

When storing a diseased part image time sequentially picked up for the same patient, the image of the entire diseased part picked up for the first time is stored in an entire image storage device 9 by an image storage part 7. Concerning the image picked up after the second time, the image of difference between a required partial image segmented out of that picked-up image by an image segmenting part 5 and the correspondent part of the entire image picked up for the first time and stored in the entire image storage device 9 is stored in a partial differential image storage device 10 by the image storage part 7.