PURPOSE: To investigate the statistic characteristic of a fixed and a moving target while improving an S/N ratio, by using mixers in combination for canceling almost all phase noises generated in a device.

CONSTITUTION: A reflected-wave receive signal 1 from a target irradiated with an electromagnetic wave and the output signal of a voltage-controlled local oscillator 37 are converted into an IF signal 5 by a mixer 32. Then, a frequency spectrum wherein a transmit signal 45 and phase noise cancel each other among various frequency spectra generated when the transmit signal 45, output of a voltage-controlled oscillator 48, output of the oscillator 37, and IF signal 5 are supplied to a mixer 40 is assumed as an IF signal 6. The signal 6 is supplied to a frequency discriminator 35 to detect the frequency shift of the receive signal 1, and the detection output is supplied with negative feed back to the oscillators 37 and 48 which have nearly equal frequency modulation sensitivity, tracking the receive signal.