An audio signal output device is disclosed in which optical signals are not output when a plug is not connected to an S/PDIF output terminal. When a plug is not connected to the S/PDIF output terminal, a fitting metal part does not contact a detection pin, and a connection detection signal is therefore 12V. As a result, a PNP transistor and an n-channel MOS transistor are both OFF, a power supply voltage of 5 V is not supplied to a drive IC, and optical signals are not output.