A relay device includes: memories, each memory being operable to store at least a data pair formed of a MAC address and a port number; a search unit to search only amongst ones of the memories having valid data pairs when searching for a port number based upon a MAC address; a data moving unit to move valid data pairs to different locations within the plurality of memories in order to reduce a total number of memories, amongst the plurality thereof, having valid data pairs; and a power supply controller to selectively stop supplying power to ones of the memories storing only invalid data.