PURPOSE: To receive data communication and voice communication through one line by selecting and changing over whether a MODEM built in a called party with telephone function as the data communication mode is used or a speech function section built in the MODEM with telephone function is operated for speech communication depending on the discriminated communication mode.

CONSTITUTION: In case of data communication, since a control section 62 at start side sends a dial signal to the called party and a communication mode signal is sent, the called party can decide whether or not the incoming call is used for data communication or call depending whether or not the communication mode signal is detected. Based on the discrimination, the MODEM 5 with telephone function is switched into the data communication mode or the call mode. Thus, both the data communication and call are received by one telephone circuit and communication is applied in each mode.