Communication using IPv6 is carried out, and conversion is given to a prefix of an IPv6 address in a firewall. A security channel for mutual authentication with an out-of-home apparatus or the like is carried out by the firewall, and only identification of an in-home apparatus is carried out on an in-home network by the firewall. A PC is connected to a PC in-home network different from the in-home network, and communication between the PC and the in-home apparatus is always carried out via the firewall.