It is an object of the present invention to protect a copyright of a content by suppressing creation of illegal copies of the content and prevent a content from being transmitted beyond a range of personal use in a process to transmit the content through a wire or wireless LAN. Before transmitting a content from a content transmission apparatus to a content reception apparatus, the content transmission apparatus and the content reception apparatus authenticate each other. In the authentication, a timer measures a time interval between a transmission of an authentication request and a reception of an acknowledgement of a reception of the request or between a transmission of a response to a received authentication request and a reception of an acknowledgement of a reception of the response. If the time interval does not exceed an upper limit, a content encrypted by using a shared key is transmitted from the content transmission apparatus to the content reception apparatus, and the address of the content reception apparatus as well as apparatus information unique to the content reception apparatus are cataloged in the content transmission apparatus. Thus, in order to transmit another content, the content is merely encrypted prior to the transmission without measuring a time interval.