A DHCP server 8 dispenses an IP address in response to a request from a terminal equipment 1. An authentication server 3 receives an authentication frame transmitted from the terminal equipment 1 using the dispensed IP address as a sender address and authenticates the terminal equipment 1. Upon completion of authentication, the authentication server 3 informs a registration information database 22 of an authentication hub 2 of communication permission for the terminal equipment 1. In the authentication hub 2, a frame receiving circuit 21 receives a transmission frame transmitted from the terminal equipment 1. The authentication hub 2 refers to the registration information database 22 on the basis of sender information of the transmission frame, determines transmission, rewriting-and-transmission, or discarding for the frame, and sends the transmission frame to a transmission buffer 23 if transmission or rewriting-and-transmission is permitted for the frame.