PURPOSE: To discriminate a target, by detecting the change quantity of the receiving intensity of an antenna by the scanning of beam and integrating said change quantity within a predetermined time.

CONSTITUTION: A duplexer 1 guides the transmission signal of a transmitter 2 to an antenna 3 and guides the receiving signal of the antenna 3 during a period of emitting no transmission signal. A differentiation circuit 5 outputs the differentiation signal of receiving intensity and an absolute value circuit 6 outputs the absolute value thereof and an integrating circuits 7 integrates the absolute value signal within a predetermined time to output an integration signal. A discrimination circuit 8 outputs the integration signal as a target discrimination signal only when said signal exceeds a predetermined value. Therefore, a target having a complicated shape can be discriminated from a reflective body having a simple shape.