PURPOSE: To improve the reliability of the measured results of a synthetic aperture radar, by calibrating the resolution of the synthetic aperture radar in the bearing direction together with the resolution in the distance direction by using a transmitter-receiver having a built-in dummy receiving signal.

CONSTITUTION: A synthetic aperture radar loaded on a spatially moving body recognizes a target by receiving radio waves reflected by the target while radiating radio waves and synthesizing the received signals into plural pictures by means of a processor 8. At the time of target recognition, a dummy receiving signal generating means 1 generates a dummy receiving signal, to which frequency variation accompanied by the movement of the moving body is added, with respect to a transmitting reference frequency. Then a coupling means 2 adds the dummy receiving signal to the output of a radio wave transmitting- receiving means 4 and outputs the output of the means 4 to a receiving means 5.