PURPOSE: To reduce the noise level coming from a powe supply of an IC device by amplifying an output of a low gain filter amplifier in the IC device for an intermediate frequency amplifier circuit at an externally mounted amplifier to the IC device and using its output to activate a squelch circuit.

CONSTITUTION: An intermediate frequency signal SIF is inputted to an IC device 2 for intermediate frequency amplification and amplified, then outputted as an audio signal SA after demodulation. The signal SA is inputted to an output amplifier circuit 6 via a mute circuit 5, subjected to power amplification and then outputted. Only a prescribed frequency band signal is extracted from the signal SA by a noise amplifier 3 comprising impedance elements Z1, Z2, a low gain filter amplifier 1 and the externally mounted amplifier circuit 3, amplified, its output is rectified (4), inputted to a squelch comparator CMP7 in the device 2 and compared with a reference voltage VREF. When an output of the circuit 6 is larger than the voltage VREF, the CMP7 outputs an H level, controls the circuit 5 to block the output of the signal SA. Since the amplifier 1 has a low gain, the noise level in the device 2 is low and the invasion from the power supply is less.