The invention is to solve the problem in that mutual communication between an IPv6-capble device and an IPv4-capble device has not been carried out in a system wherein the IPv6-capble device and the IPv4-capble device are mixed. An entry of a live list is retrieved when SM Device Annunciation is received from the IPv6-capble device, and a transmission IPv4 address is acquired from an IPv4 address pool if the entry is not found, thereby preparing translation rules so as to be stored in a translation rules storage section, while preparing an entry to be registered in the live list, whereby an IP address in a message is translated with reference to the translation rules. Further, a timestamp of the entry is updated every time when the SM Device Annunciation is received. Even if the address is contained in the message, the mutual communication between the IPv6-capble device and the IPv4-capble device can be carried out, and devices connected to the system can be controlled.