To provide an image data processing system that can efficiently utilize a user area of an image data storage device.

A part of a storage area of a hard disk loaded on a server computer 1 is provided to a user of a digital camera 2 as a user area. The user can utilize the user area as two areas consisting of a cache area where the newest image data is overwritten by erasing the oldest image data when the user area is deficient and of a storage area where the other image data cannot be erased. The user can set the ratio of the cache area to the storage area by utilizing the digital camera 2 possessed by the user as desired by the user. Whether the image data is stored in the cache area or the storage area is instructed by the digital camera 2 for every photographing time.