PURPOSE: To inform an opposite terminal device number to a terminal device without complicating the processing of a central control section by adding a terminal number storage function and a control function provided corresponding to a terminal device.

CONSTITUTION: When a terminal device 11 makes transmission, a line exchange 10 receives transmission information and an opposite party number through an interface circuit 22 and informs an incoming call to an interface circuit 23 of the opposite terminal device 12 by the control of a central control section 13. Before the terminal device interface circuits 20, 21 calls the opposite terminal device 12, a channel switch path is utilized so as to transmit and receive the subscriber number of a bothway terminal device. Moreover, control circuits 32, 33 receive the opposite terminal device number transmitted from transmission circuits 29, 28 of the opposite terminal device at reception circuits 30, 31. Then the control circuits 32, 33 transmit the opposite terminal device number received by the reception circuits 30, 31 to the terminal devices 11, 12 by using the opposite terminal device number transmission circuits 24, 25.