PURPOSE: To surely correct a multipath distortion, by correcting an input signal in accordance with the difference between the output signal of a low-pass filter and the signal which is the arithmetic mean of the output signals of a (+) side and (-) side envelope detecting circuits.

CONSTITUTION: An adder 2 outputs the difference between an input signal (a) and correcting signal (h). The output signal (b) of the adder 2 is supplied to a low-pass filter 3, (+) side envelope detecting circuit 4, and (-) side envelope detecting circuit 5. The filter 3 outputs a signal (c), from which noise frequency components are attenuated. On the other hand, the output signals (d) and (e) of the circuits 4 and 5 are averaged by means of an adder 6 and subtractor 7 and, as a result, a signal (f) is outputted. An adder 8 outputs a signal (g) which is the difference between the signals (f) and (c). Since the signal (g) is superposed upon the signal (a) and proportional to the level of noises, the correcting signal (h) is obtained when the signal (a) is amplified at an amplifier 9. The corrected signal (b) is outputted from an output terminal 10.