Various services for a mobile communication network or an IP network are implemented by processing necessary information suitably in accordance with a service type so as to exchange the information to a service control device and transmitting the results of the service process by the service control device to the mobile communication network or the IP network, for a service request from the mobile communication network or the IP network. A gateway device of the present invention retains a signal defining various rules or policies received from the service control device, judges a service type and a destination requested from the service request signal by the various rules or policies for the service request signal transmitted from a communication terminal of the mobile communication network or the communication terminal of the IP network, performs protocol conversion on the service request signal in accordance with the service type, and transmits the service request signal to the corresponding destination.