PURPOSE: To assure the capture range and to improve the stereo separation degree and high band distortion, by controlling the time constant of loop filter based on the detection signal of stereo pilot signal.

CONSTITUTION: A phase comparison circuit 11 phase-detects the FM signal based on 19kHz frequency dividing signal, and the phase difference detection signal is fed to a DC amplifying circuit 13 to output stereo detection signal. In case of monaural broadcast or stereo broadcast reception, until the PLL circuit is locked, the stereo detection signal is a low potential, the relay RL is not operated, and since the switch SW is off, the time constant of the loop filter 3 is small. When the PLL circuit is locked state, the stereo detection signal is at high potential, and since the relay RL is operated and the switch SW is on, the time constant of the loop filter 3 is greater.