A relay device includes a first signal reception unit receiving a signal from the outside, a first radio communication unit transmitting the signal by radio that is received by the first signal reception unit, a second radio communication unit provided separately from the first radio communication unit and transmitting/receiving a signal by radio, a detection unit detecting transmission/reception of the signal by the second radio communication unit, and a first inhibition unit inhibiting, during a period in which transmission/reception of the signal by the second radio communication unit is detected by the detection unit, transmission of the signal by the first radio communication unit. Thus, communication by means of a plurality of communication units can efficiently be accomplished.