To alter routing information on an existing network in real time by sending additional network address information and WAN port IP address information on additional network equipment as information routed to a request- source network.

The additional network equipment 11 is provided with a processor 12, whose request-destination IP address information retrieval processing part 16 retrieves whether or not a request-destination IP address is present and generates routing change information based on the information set previously in a routing generation management table 19 when corresponding equipment is present. This alteration information sent to a processor 10 of the existing network equipment 1 and only when existing routing information is not present as information routed to the request-source network, routing to a route which is not used by the existing routing information.