PURPOSE: To exactly discriminate whether a received signal is a facsimile signal or a voice signal by exactly measuring the pulse width of a facsimile transmission signal regardless of the size of a received signal level.

CONSTITUTION: A facsimile transmission signal detecting circuit 15 detects a CNG signal(facsimile transmission signal) transmitted at first according to a facsimile communication procedure. A detection circuit 16 operates the envelop detection of the CNG signal. Since a pulse width measuring circuit 17 which measures the pulse width of the detection signal outputted from the circuit 16, starts measurement at the time of the rising of the waveform of the detection signal, and ends measurement at the time of the falling from the peak value in a prescribed level. A connection control circuit 13 connects a facsimile signal processing system with a telephone line 1 when the measured value of the pulse width from the circuit 17 indicates the pulse width of the CNG signal transmitted at first according to the facsimile communication procedure.