PURPOSE: To attain sound indication in a stable state by cutting off a high frequency component of a sound signal through the decreased channel separation when an electric field strength of the sound signal is high and external noise is frequently inputted and keeping the control while external noises last.

CONSTITUTION: A noise detection circuit 6 detects multi-path noise and it is integrated by an integration circuit 10. A short circuit 9 is open when the integration value is lower than a threshold level to inhibit channel separation and high frequency component elimination in a stereo broadcast. Upon the receipt of noise on the other hand, a short circuit 8 is closed to connect other terminals of registers 12, 14 to ground thereby reducing outputs of SNC and HCC signals from output terminals 11B, 11C. When the noises last for a prescribed time, an output of the integration circuit 10 exceeds a threshold level of the short circuit 9, which is closed and a voltage of the SNC and HCC signals from the output terminals 11NB, 11C. Thus, a multiplexer circuit 4 decreases the separation and cuts off the high frequency component.