To permit only the specific device to reproduce digital data such as video images and sounds.

Encryption key information read by an authentication reading means is written into an encryption key information storage medium having this built-in device, the writing date/time is acquired as registration date/time information from a date/time measuring means, and encryption key-related information having four items of information, i. e. registration date/time information, and medium unique information, issuing time information and creating date/time information which are read by the authentication reading means are written into the encryption key information storage medium. The encryption information read from the encryption key information storage medium is used to generate an encryption key. Input digital data are made into encrypted data by using the encryption key. The encrypted data are written into the data storage medium, and the encryption key-related information read from the encryption key information storage medium is written into the data storage medium.