A sound volume set-point value set by the variable resistor 1 is converted into a sound volume set-point value signal by a sound volume set-point value detecting section. A control signal generating section rectifies an input signal and adds it to a sound volume set-point value signal, thereby generating a control signal less fluctuated, and the amplification factor of amplifying section is adjusted by the control signal. The input signal is amplitude limited by this, to thereby prevent an output sound from being distorted. When the input signal is low in level, the amplitude limiting operation of the amplifier is stopped, to thereby retain a dynamic range of the original signal. Through the fluctuation suppression of the control signal, the unnatural feeling given to the listener when the amplitude limiting operation starts or stops is also lessened.