An adder mixes an L-channel sound signal and an R-channel sound signal with each other and then outputs a mixed signal. A switching unit performs a switching operation such that, if power is being supplied to loudspeaker amplifiers, the L-channel sound signal and the R-channel sound signal are respectively supplied to the loudspeaker amplifiers, and if power is not being supplied to the loudspeaker amplifier, an output signal of the adder is supplied to the loudspeaker amplifier. A power down control unit forces a loudspeaker amplifier to which power is not supplied and a preamplifier for driving the loudspeaker amplifier to be in a power-down state.