A demodulator according to the present invention is the demodulator that demodulates a plurality of received symbols having different amplitude of carrier wave. The demodulator includes an amplitude value calculation unit that calculates a received symbol amplitude value by adding an absolute value of in-phase component and an absolute value of quadrature component determined from the amplitude of the carrier wave in the received symbol. Further, the demodulator includes a demodulation unit that detects a change of the received symbol amplitude value calculated by the amplitude value calculation unit, and demodulates the received symbol based on the detection result.