When a user wishes to play purchased content data by a playing terminal, a registration database server authenticates a user ID. Furthermore, when the playing terminal requests a content server to establish communication, the content server authenticates the playing terminal to thereby establish communication only with the playing terminal of which the user ID authentication and terminal authentication are correct. Consequently, the content data is prevented from being copied to another playing terminal which is owned by a third party, and thus the copyright of the content data can be protected.