Abstract: A phase monopulse radar system includes a transmitting antenna that transmits a transmission signal, a plurality of receiving antennas that receive reflected waves of the transmission signal as received signals, a target azimuth detecting unit that detects an azimuth of a target based on a phase difference of the received signals received by the receiving antennas, a phase inversion determining unit that determines whether a phase inversion occurs to any one of the received signals, at around a peak frequency of a frequency spectrum of the received signal, and a detection object excluding unit that does not use an azimuth based on the phase difference as a target azimuth, when the phase inversion determining unit determines that the phase inversion occurs.