PURPOSE: To eliminate the need for the security of an information channel by including control information representing whether or not entering a communication protocol via an information channel in a setup message and sending a data only through a control channel.

CONSTITUTION: A terminal equipment 20 operates a key board input device 16 to decide information representing whether or not a communication protocol through an information channel and information to be set to a user/user information section together with an incoming address or the like to make a call to an ISD network and sends the information through a D-channel being a control channel of a line 30. The ISD network generates the information received from the terminal equipment 20 as a format of a setup message and sends it to the incoming terminal equipment 20 through the D-channel. Since the control information representing whether or not the communication protocol via the information channel is included in the setup message, an interrupt procedure is proceeded after the setup message is received by using the control information.