To reduce the whole data quantity while keeping the incidental information of a DICOM file for a prescribed period of time.

An image server 30 receives a DICOM file which includes image data on medical-use images and incidental information relating to the image data from a modality 10, divides the DICOM file thus received into an image data file (a wide-use image file) and an incidental information file (a DICOM header file), correlates these files with each other, and stores them in a storage part. When a storage period of the general-purpose image file elapses over the first period, the image server 30 deletes the image file from the storage part. When a storage period of the DICOM header file elapses over the second period which is longer than the first period, the image server 30 deletes the DICOM header file from the storage part.