PURPOSE: To specify an incoming terminal at the reception side without notifying an IP address from the transmission by making a use of a dial-in service giving a plurality of numbers to one communication channel.

CONSTITUTION: A plurality of numbers or ISDN addresses are given to one user network interface set through a subscriber line terminal equipment DSU, a plurality of communication equipments 1-3 are arranged corresponding to it. (b) At the time of calling, when ISDN address, for example, 045. 777. 1001-1003 are given from ISDN, a communication equipment 2 is selected to set a call. ISDN addresses 045. 777. 1001-1003 are given to one communication equipment 11, IP addresses 100, 200, and 300 for a plurality of terminals WS1-WS3 corresponding to these are set. Thus, the IP address terminal corresponding to the ISDN address are specified from among WS1-WS3.