It is determined whether phase noise and parasitic oscillation take place on the basis of a carrier-to-noise (C/N) ratio calculated with amplitudes in an amplitude direction of signal points of a reception signal and a C/N ratio calculated with amplitudes in a phase direction of the signal points of the reception signal. Further, when it has been determined that phase noise and parasitic oscillation take place, an alarm is displayed on a screen. When it has been determined that phase noise and parasitic oscillation take place, the phase of a demodulation circuit is compensated based on the detected phase noise.