PURPOSE: To accurately perform the judgement of clutter, by leading out the expansion of a reflected wave by correcting the positional informations of the front and rear edges of the radar video signal, received by electronically scanningly a phased array antenna, on the basis of a scanning angle.

CONSTITUTION: A phase array antenna 7 emits radar pulses from a transmitter- receiver 2 to a space and the reflected signal from a target is received by the transmitter-receiver 2 to be inputted to a detector 3. At the same time, the scanning angle of the antenna is also inputted to the detector 3. The detector 3 detects the front and rear edges of a radar video and outputs antenna scanning angles Q1, Q2 corresponding thereto to a correction circuit 8 as front and rear edge positions. The correction circuit 8 judges a scanning direction from the magnitude of Q1, Q2 to correct a beam width and inputs the corrected beam width to a target signal width detection circuit 4 and clutter is judged on the basis of the calculated target signal width by a clutter judge circuit 5. By this method, clutter can be accurately judged regardless of the scanning angle of beam.