In an apparatus for encrypting an information signal into an encryption-resultant signal, a first encryption key peculiar to the present apparatus is generated. Key information is read out from a replaceable recording medium. A decision is made as to whether or not the read-out key information has been generated by an apparatus different from the present apparatus. A second encryption key is generated in response to the read-out key information when it is decided that the read-out key information has been generated by an apparatus different from the present apparatus. One is selected from the first encryption key and the second encryption key as a final encryption key. An information signal is encrypted in response to the final encryption key.