PURPOSE: To eliminate expensive interface for automatic transmission and simplify and economize the system by unifying interface for automatic transmission and succeeding data communication.

CONSTITUTION: Selection number of an object of communication is inputted from the inputting section 26 of a terminal device 23 and accumulated in a memory 27, and at the same time, call display is transferred from a signal interface section 24 to the signal inputting and outputting section 21 of a network controlling device 15 through a signal interface line 22. Thereafter, when exchange of call display and dial tone detection signal and exchange of selecton number with subscriber's circuit are completed by a controlling section 19, the controlling section 19 gives reply monitor command to a circuit controlling section 16. Then, it commands sending out of carrier to an MODEM section 17, and makes exchange of reply and carrier. Data sends a signal from the terminal unit 23 to the MODEM section in a signal selecting section 20 and makes exchange by one interface.