A PSK modulator 20 applies digital modulation processing to an RF wave supplied from an RF wave oscillator 22, by means of phase shift keying (PSK) based on a periodical signal sequence supplied from a pattern generator 24, to thereby generate a continuous wave. The continuous wave output from the PSK modulator 20 is delayed in delay circuits 26I and 26Q and is then supplied, as a reference signal, to each of mixers of a receiving mixer 30. Each of the delay circuits 26I and 26Q delays the continuous wave by a delay amount in accordance with a depth of a target position and outputs a delayed reference signal. Thus, demodulation processing is performed with a correlation between a reception signal from the target position and the reference signal being enhanced, and Doppler information from the target position is selectively extracted by a Doppler information analyzing unit 44.
