PURPOSE: To simplify the constitution of a receiver, by detecting whether a signal applied to an input port is an FS system or an MS sytem depending on the level of an FS signal component extracted at a receiving filter for outputting automaticaly a signal to an output terminal.

CONSTITUTION: Only an in-band signal is extracted from the FS signal from a receiving input terminal 1 at a receiving filter 4 via a hybrid coil 2 and a signal amplifier 3 and amplified to a saturation level at a limiter amplifier 5. An output of the amplifier 5 is demodulated at a signal demodulator 6, its output is applied to an S-P signal converter 8 and a parallel data is outputted to a data output port 16. Further, a part of the output of the amplifier 5 is applied to a transistor (TR)9 having a relay 10 via a signal detector 7. On the other hand, an MF signal from the terminal 1 is decoded at an MF signal decoder 12 and applied to a gate circuit 13 and outputted to a port 16. Further, the gate 13 is controlled with the level of the FS signal detected at the TR9 and a strobe signal is outputted via a contact 15 of the relay 10.