To provide a control technology which can suppress an unpleasant click sound occurring upon releasing a standby in an audio amplifier, and can boot up a reference voltage that is supplied to the audio amplifier quickly.

The audio amplifier includes: differential amplifier circuits 11, 12 for inputting an audio signal into one input terminal, and inputting an analog reference voltage into the other input terminal; a reference voltage generating circuit 14 for generating the analog reference voltage; and a power supply switch for supplying/shutting off a power supply voltage to/from the differential amplifier circuits and the reference voltage generating circuit, respectively. In the audio amplifier, there is provided a charging-up circuit 42 which generates a 1/2 voltage of the power supply voltage in a steady state, and also boots up a potential of a node generating the 1/2 voltage to a given voltage potential close to the 1/2 voltage within a shorter time than a cycle equivalent to a maximum frequency of an audible area when the power supply switch is changed from an off state to an on state.