To construct an easily portable and also economical system that makes a player enjoy digital contents at any time in any place and that sufficiently resists application as defence against illegal usage, by decoding the processed digital contents with a content key and also extending and reproducing them.

A player 1 is provided with at least a common key cipher decoding circuit 24 decoding the ciphered digital contents through the use of the content key, an extending circuit 26 being an extending means for extending the compressed digital contents and a D/A converting circuit 27 converting digital data into an analog signal. When the player 1 is the one who is registered in the system, he can freely copy the ciphered contents so as to appreciate the contents only by obtaining the content key. Therefore, the ciphered contents are easily installed in storage media.