A user key storage unit stores at least one user key corresponding to usage authorities of image data. A first encryption unit encrypts the image data using a first encryption key. A second encryption key creation unit creates a second encryption key assigned to each usage authority. A key-storage data creation unit creates a key-storage data for each usage authority by encrypting the first encryption key and authority information using the second encryption key. A user-supplementary data creation unit creates user-supplementary data for each user key. A device-supplementary data creation unit creates device-supplementary data for at least one usage authority and for at least one device key. A data output unit outputs encrypted image data with the key-storage data, the user-supplementary data and the device-supplementary data.