PURPOSE: To enable high precision measurement with a relatively simple configuration at a low cost in an ordinary room.

CONSTITUTION: A transmitter/receiver 1 transmits electric wave and receives reflection wave as well. At that time, either the transmitter/receiver 1 or an object 2 to be measured is moved along a straight line connecting both. Thus, the reflected wave received by the transmitter/receiver 1 contains Doppler frequency deviation Δf that accompanies movement. At the transmitter/receiver 1, the Doppler frequency deviation Δf is detected, and further, through Fourier transformation with the Doppler frequency deviation Δf, transformed into frequency spectral. With this frequency spectral, peak level caused only by the object is obtained.