When image date has been decomposed into a plurality of components, and a plurality of components of the components have been encrypted, the encrypted image file must be able to be used without confusion. On a component decomposing means, image data is decomposed into a plurality of components for the hierarchical levels, for example. On an encrypting means, a plurality of components of the components are encrypted. And, on an encrypting information preparing means, encrypting information H concerning the contents of this encryption is prepared, and from the encrypted components and the non-encrypted components, and the encrypting information H, an encrypted image file F is generated on an encrypted image file generating means. When the encrypted image file F is to be decrypted, the encryption contents of the encrypted components can easily be grasped by referring to the encrypting information H.