A terminal (101) includes interfaces for communication with a mobile network (102) and a wireless LAN (103). A first IMS server (107) performs IMS call control processing relating to terminals located in the mobile network (102) and a second IMS server (111) relays a signal relating to IMS call control processing concerning terminals located in the wireless LAN (103). These IMS servers search for a mobile network packet gateway (106), a packet data gateway (110), and a gateway to be controlled by a route change request for requesting change of a packet transmission path and relay the route change request. The route change request provided from the terminal (101) is relayed by the IMS servers to provide the change request to all networks specified. The packet transmission path is changed by the gateway in accordance with the request. Thus, the terminal having the interfaces for both of the mobile communication network and the wireless LAN can select a network to use for each communication port.