PURPOSE: To schematically detect the coming direction of a radio wave signal by setting a non-directional antenna at each vertex of a regular triangle and detecting the reaching time of the radio wave signal at each point.

CONSTITUTION: Three non-directional antennas Ia-Ic are set at respective vertices of a regular triangle. Wave signals input to the antennas Ia-Ic enter corresponding target separating circuits 2a-2c and, after being A/D converted, the signals are separated every radio wave source based on the frequency, pulse repetition frequency and pulse width. Moreover, blip detecting circuits 3a-3c detect the time when the amplitude shows its peak as the reaching time of a blip, and output the time together with the data of the frequency or the like detected at the circuits 2a-2c to a target comparing circuit 4. The circuit 4, correlating the data from the circuits 3a-3c, detects that it is a target coming from the same radio wave source. Further referring to a memory 5, the circuit 4 extracts the scanning direction of data with which the frequency or the like agrees. A direction detecting circuit 6 detects the coming direction of the radio wave schematically from the reaching time of the blip and the scanning direction detected at three points and sent from the circuit 4.