An apparatus (10) for adjusting sound volume for an audio system includes a controller (101) connected to an amplifier (40) of the audio system for controlling amplification of the amplifier, and a first circuit (102) for adjusting the sound volume. The controller includes a microprogrammed control unit (1010), a random-access memory (1012), and an electrically erasable programmable read-only memory (1014). The first circuit includes an attenuation circuit (1022) connected to a tuner of the audio system for attenuating input audio signals, and a switch (1024). An input end of the switch is connected to the tuner and an output end of the attenuation circuit, and an output end of the switch is connected to an audio processor (30) of the audio system. The apparatus enables a user to freely adjust an average level of sound produced by the audio system, and simultaneously avoid being bothered by loud transmissions.