To efficiently delete unnecessary image data by easily discriminating between necessary image data and unnecessary image data.

When this print system 100 deletes a large amount of image data stored in a print server 30, the image data are given order IDs and managed according to the order IDs as to the date when they are stored in the print server 30 and whether or not prints are purchased. A predetermined period of time after the image data has been stored, the image data whose prints are left unpurchased are deleted from the image memory 39 of the print server 30 as unnecessary image data.