An image data processing apparatus that restricts the output or transfer of image data stored in a folder comprising a box to another box. In order to improve the maintenance of confidentiality, the image data processing apparatus includes multiple folders or boxes 141, 142, non-volatile storage means 141 that stores image data and attribute information that prescribes the handling of the image data in one of the folders, and control means 17 that controls the handling of the image data based on the attribute information when an instruction to process image data stored in a folder 141, 142 is received from the user.