File encryption device, file decryption device, system, and program

A file encryption device is provided with: an encryption key acquisition unit for acquiring one or more encryption keys set for each of one or more users having permission to access an electronic file; a file encryption unit that encrypts an electronic file; a supplementary information encryption unit that uses one or more of the encryption keys to encrypt supplementary information including a file decryption key required to decrypt the encrypted electronic file; and an output unit that associates the encrypted supplementary information with the encrypted electronic file and outputs the result.