PURPOSE: To eliminate the need for a change in the constitution of a computer system when the constitution of a terminal equipment side is revised by retrieving a cross reference list of network addresses at the terminal equipment side and the computer system with respect to a received network address selection request so as to select an opposite network address possible for communication.

CONSTITUTION: A network address selection request reception means 21 receives a network address selection request from a terminal equipment 11 and requests the selection start of a communication enable opposite network address to a network address selection means 22. The network address selection means 22 selects the opposite network address possible for communication with the terminal equipment 11 and applies network address selection end notice to a network address cross reference means 28. The network address cross reference means 23 references network addresses of the terminal equipment 11 and the computer system 30.