An output device to output an image and/or a sound based on a signal input from one of a plurality of external devices connected to the output device, the external devices including an HDMI source device to input an HDMI signal to the output device. The output device is configured to instruct an adjustment of sound volume of the sound output from the output device; to adjust the sound volume of the output sound in accordance with an instruction from an instruction section; to judge whether a header of an Audio InfoFrame exists in InfoFrame data in the HDMI signal input from the HDMI source device or not; and to invalidate the instruction from the instruction section during a period from time when the header of the Audio InfoFrame is judged not to exist by the judgment section to time when the header is judged to exist.