A relay device includes first demultiplexing units that demultiplex reception signals into demultiplexed signals in a narrower band, first and second multiplexing units that multiplex input signals to generate multiplexed signals, transmission antennas that transmit the multiplexed signals generated by the multiplexing units, a regenerative relay unit that modulates an information sequence obtained by carrying out demodulation processing to the multiplexed signal generated by the second multiplexing unit to generate a modulated signal, a second demultiplexing unit that demultiplexes the modulated signal into a demultiplexed signal in a band narrower than the band of the reception signal, and a switch unit that inputs the demultiplexed signals demultiplexed by the first demultiplexing units to the multiplexing units and inputs the demultiplexed signal demultiplexed by the second demultiplexing unit to the first multiplexing units.