Patent ID: 8233640

Claim:
A sound output device outputting sound according to an audio signal fed thereto, comprising: an audio signal amplifying circuit that amplifies the audio signal with an amplification ratio according to a volume adjustment signal and a switching signal; a volume adjuster that is operated by a user in a predetermined manner and that determines a ratio of volume of the sound to predetermined reference volume by outputting the volume adjustment signal according to how the volume adjuster is operated by the user; a time detector detecting that a predetermined time has come; and a reference volume adjuster adjusting the reference volume by outputting the switching signal according to a detection result of the time detector, wherein the audio signal amplifying circuit includes: an amplifier that includes a power supply terminal and that amplifies the audio signal with an amplification ratio according to a voltage fed to the power supply terminal; and a voltage switching circuit that outputs a voltage corresponding to a state of the switching signal; and the audio signal amplifying circuit adjusts the voltage outputted from the voltage switching circuit according to the volume adjustment signal, and feeds the adjusted voltage to the power supply terminal.