PURPOSE: To reduce the deterioration of a signal by removing an impulse noise from an FM demodulated signal in the case of a weak electric field.

CONSTITUTION: An impulse noise a' is extracted from an input signal 1 through an HPF 2, a gate pulse (b) is generated from an MV 5 by delaying the noise a', the input signal is also applied to delay circuits 3, 4 to delay it, the gain of the impulse part is turned to '0' through gate circuits 11 to 13, and the amplitude values E1, E2 of the leading edges of signals are extracted. On the other hand, a slowly rising rectangular wave (h) is extracted from the gate pulse through a saw tooth generating circuit 8 and a gate circuit 9 and a slowly falling triangular wave (m) is extracted through an MV 7 and a subtraction circuit 10 so that the amplitude values of both the signals (h), (m) are set up to E1 and E2. Then outputs (f), (l) from the gate circuits 11, 12 are held by respective box cars 14, 15 as pulses f', l' with width τ2, signals (i), (n) with amplitude E1, E2 are obtained respectively through multiplier circuits 16, 17 and added to the output (k) of the gate circuit 13 through a synthesizing circuit 18 to execute the linear interpolation of the leading and trailing edges of the part lacked as the impulse part by the gate circuit 13.