PURPOSE: To prevent howling by performing sound volume control according to an ambient noise except the output sound component of an electroacoustic transducer.

CONSTITUTION: An audio signal from an audio signal generating source 1 is passed through a band eliminator 7 to remove the components of several frequency bands, and only the remaining components are led to the electroacoustic transducer 4 to be outputted as a sound. A noise in the outside where the electroacoustic transducer 6 is installed is transduced into an electric signal by the acoustoelectric transducer 6 and the signal is led to a band extractor 8 to extract only the same components with the frequency bands eliminated by the band eliminator 7. The output sound of the electroacoustic transducer 4 is controlled in responding to the output frequency components of the band extractor 8.