PURPOSE: To eliminate distortion due to a side band, noise due to a failure in phase locking, etc., by making the extent of attenuation only in a range where an S curve is present the outside of a muting band greater than the extent of muting attenuation where no electric field is normally etstablished during detuning.

CONSTITUTION: A level detector 14 receives part of an IF signal from an IF amplification stage 2 to output a DC voltage proportional to a received electric field. In an intermediate electric field, the output of the level detector 14 nearly in a tuning state is as shown by (b) at an output terminal 15 for a signal meter. A muting voltage shown by (c) is outputted to a muting output terminal 10 at the outside of a muting band (25). This voltage and the output of said output terminal 15 are supplied to an AND circuit 16, and consequently such a muting voltage that the extent of muting attenuation greater than when no electric field is established normally is obtained in ranges 26 and 27 shown by (d) appears at a muting control terminal 11.