PURPOSE: To prevent generation of noise by providing two low-pass filters having different time constant in a PLL circuit in an FM demodulator and using the low-pass filter having the larger time constant when an input is decreased.

CONSTITUTION: An FM modulation signal A is inputted to a terminal 4. The signal A is fed to a phase comparator 1, where the signal is compared with an oscillation signal of a voltage controlled oscillator VCO2. An output of the comparator 1 is inputted to the 1st low-pass filter 3. An output of the low-pass filter 3 is inputted to the VOC2 and also led to an output terminal 5 as a demodulated output. The signal A is inputted also to a carrier level detector 8. When the signal A is decreased, a switch is changed over by a switch control circuit 9 and the circuit is connected to a low-pass filter 6 having the larger time constant. The changeover is attained also by a mute command.