PURPOSE: To miniaturize a part to execute ringer detection and the detection and transmission of communication data by switching a switch termination resistor, which is connected to the secondary side of a transformer, to high resistance/low resistance and detecting a ringer and the communication data.

CONSTITUTION: It is detected and decided by a direct current detecting circuit 3 whether a direct current component flows to a line (under standby) or not. In the case of YES, a switch termination resistor R1 is switched to high resistance (>>600Ω) and operation is set to a ringer detectable state. Then, it is detected whether the ringer of a calling signal from an F network is detected or the ringer of 16Hz to be the calling signal of a telephone set is detected. In the case of YES, the resistor R1 is switched to the low resistance (almost 600Ω). A relay 2 for line hold is turned on. Thus, a direct current loop is formed to the line and the primary side of a transformer 1 and the direct current component flows. The communication data are detected from the secondary side of the transformer 1 and sent to the secondary side and a procedure signal and a picture signal are transmitted and received with the facsimile equipment of a communication party. After that, it is decided whether communication is finished or not. When it is finished, the relay for line hold is turned off and the resistor R1 is switched to the high resistance.