PURPOSE: To optimally control a sound volume level free from unnatural feeling to a human hearing sensation by automatically adjusting the sound volume level corresponding to the noise which changes in rough proportion to the speed of the automobile.

CONSTITUTION: When the automobile runs and the speed is increased, the output voltage (audio level control signal) E of an F.V converter 22 is proportionally increased with the increase of automobile speed information (corresponding to engine speed Q) from an ignition coil 21. At this time, as an electronic volume circuit 22 adds an output signal K corresponding to a sound volume level output signal to a system output C from a car radio unit 10, the sound volume level from a speaker 15 is increased in rough proportion to the increased portion of the speed. But, when the car is decelerated, the sound volume level from the speaker 15 is decreased in rough proportion to the decreased portion of speed. Consequently, the sound volume level is controlled automatically and optimally to the increase/decrease of the noise which changes in rough proportion to the speed of the automobile.