PURPOSE: To eliminate the need for a means to adjust the amplitude after demodulation by switching a demodulation sensitivity in response to a frequency band occupied by a signal to make the amplitude of a demodulation output nearly constant independently of the deviation by a signal transmission system (frequency deviation).

CONSTITUTION: One of inputted FM signals VI divided into two at a branch point α is sent as it is as the main signal to a multiplier 11, and the other is sent to the multiplier 11 via a delay circuit 12. A mode discrimination circuit 9 applies frequency detection to an RF signal VI to discriminate whether the signal system is a recording mode at a wide band or that at a narrow band. A switch element 15 is subject to switching control by a signal from the mode discrimination circuit 9 and a delay time of the delay circuit 12 to the input signal is set to a prescribed value in response to the mode. Thus, since the demodulation sensitivity is switched in response to the frequency band occupied by the signal, the amplitude of the demodulation output is made nearly constant independently of the deviation, and a means to adjust the amplitude after demodulation is not required.