An audio controlling device generates an audio mute signal based on the level of a power-supply voltage supplied from the source equipment, whether a clock signal has been input or not, whether a digital signal has been input or not, whether a multiplier circuit is being locked or not, an error rate, whether an audio clock detection circuit is being locked or not, the presence or absence of a change in a control signal, and whether a synchronization detection circuit is stable or not. The audio controlling device applies the audio mute signal to an audio mute circuit, while applying an OSD control signal to an OSD processing circuit. The audio mute circuit is placed in a mute state or unmute state based on the audio mute signal. The OSD processing circuit provides the on-screen display of a message based on the OSD control signal.