The problem to be solved is that once copyright claimed AV data is passed to application software, the application software can freely process the AV data for recording, etc., defeating the purpose of copyright protection. The invention provides a computer which comprises a system section 12 and an application software section 13, and which takes in copyright claimed, encrypted data via a digital interface 1 for processing therein, wherein the system section 12 judges that the application software section 13 is legitimate application software for the protection of copyright, and if the application software is a legitimate one, the system section 12 passes a key for the encrypted data to the application software section 13.