For achieving the protection of copyright, by suppressing illegal copy production thereof, in particular, when transmitting contents with using a wired or wireless LAN, as well as, for preventing the transmission of contents from deviating from a range of a personal use thereof, a contents transmitter apparatus and a contents receiver apparatus make an authentication, mutually, before transmitting contents therebetween. At the time when conducting this authentication, measurement is made upon a time-period up to arrival of a receipt confirmation responding to the transmission of an authentication request or a response to the authentication; then, only in the case when this value measured does not exceed a predetermined upper value, the transmission is conducted on the contents encrypted, and at the same time, address information and equipment information unique to the apparatus are registered, thereby conducting the transmission of encrypted contents, but without conducting the time-measurement thereon, when transmitting the contents, again. Also, while conducting the time-measurement periodically, dynamic management is made on the registration information, so that the contents thereof are suitable for the network structure at the present.