In a small-scale medical facility, appropriate storage and management of medical images whose storage is mandatory for a predetermined period becomes easier. A storage terminal installed in a medical facility is connected to a mobile storage system, and image data stored in the storage terminal are transferred to the mobile storage system. The mobile storage system storing the image data is connected to an image data storage apparatus installed in an image storage center, and transmits the image data to the image data storage apparatus. The image data storage apparatus stores the image data and calculates the date of storage expiration of the image data. The image data storage apparatus stores the image data until the expiration date.