PURPOSE: To make pulse compression upon a reflected wave possible and to improve distance resolution by adjusting and setting properly element intervals of half-wavelength dipole antennas at an unequal length and an equal interval and the feed-point position of a receiving antenna.

CONSTITUTION: Pulses with narrow width sent from a transmitter are passed through a balanced-unbalanced conversion circuit 4 for balanced conversion and applied to a dipole antenna having minimum resonance length in a half-wavelength dipole antenna array 2. Then, they strike a body which reflects radio wave successively from higher frequency components, and those arrive to receiving antenna successively from higher frequency components. The receiving antenna has a balanced-unbalanced converting circuit 10 connected where a half-wavelength dipole antenna array 8 has minimum resonance length and it takes a time for a maximum frequency component to reach a power reception point, so that it aligns in phase with a low frequency component which is delayed and received at the power reception point, applied to the balanced-unbalanced converting circuit 10, and sent to a receiver.