PURPOSE: To prevent generation of transient sounds and simplify the constitution of a muting circuit used for the wave detecting system of radio receivers, by detecting signal levels at the time of strong input during a transient period and interrupting the output of a muting amplifier.

CONSTITUTION: Under a transient conditon caused when power supply is made, the receiving mode is switched to AM detection mode, etc., the signal level at the time of strong input during the transient period until an AGC signal rises is detected and given to a muting signal generating curcuit 6. A muting signal of a pulse is generated from the output terminal 56 of the circuit 6 and given to a muting amplifier 10. As a result, the muting amplifier 10 is set to the non- operating condition or the section between the input and output of the amplifier 10 is controlled to an interrupted condition during the period when the muting signal is generated. Moreover, the output terminal 58 of the amplifier 10 is maintained under a no-signal conditon during the period when the muting signal is generated.