PURPOSE: To constitute the system so that a user of a network connected to a gateway processor can execute mutually to other network without being aware of a protocol of the network of the other part of the communication by converting to communication information by a specific intermediate protocol in the inside of the gateway processor.

CONSTITUTION: A gateway processor G is connected to each of networks A-D by using access points P-A-P-D. In such a state, from one of the networks A-D, one of the access points P-A-P-D connected thereto receives communication information by one of protocols X-Z, W peculiar to one of its networks A-D, and converts it to communication information by an intermediate protocol T peculiar to the gateway processor G. In such a way, a user of the network connected to the gateway processor G can execute mutually a communication to the other network without being aware of the protocol of the network of the other party of the communication.