A differential signal output device is disclosed that outputs transmission data as a differential signal. The device includes a first differential signal generation circuit that amplifies a signal representing the transmission data and generates the differential signal from the amplified signal; a dummy data generation circuit that is synchronized with a reference clock of the transmission data and generates dummy data that change only in a bit where the transmission data do not change; and a second differential signal generation circuit that amplifies a signal representing the dummy data and generates another differential signal from the amplified signal.