PURPOSE: To realize a constant amount of data exchange defined by a user-to- user information element, at low communication cost.

CONSTITUTION: A terminal control information detecting circuit 2 when receiving a call setting message in a call control message from an ISDN basic interface at the time of termination detects control information to an ISDN communication terminal equipment from the user-to-user information element of additional service without any call setting. Control information obtained by a terminal control information detecting circuit 3 is stored in a memory 3 dedicated to terminal control. A terminal control circuit 4 performs control according to the control information stored in the memory 3. A control result transmitting circuit 5 transmits the control result of the terminal control circuit 4 with the user-to-user information element of a disconnection message in the call control message.