To provide a detector for an electric wave arrival direction detecting system and its control method, allowing accurate detection of the direction of the maximum received signal strength at all times.

Electric waves of transmission pulses emitted by a transmitter 1 are received while changing the direction of a receiving beam of the electric wave arrival direction detector 10 over all azimuth angles in detecting the maximum received signal strength, thereby, an electric wave arrival direction is detected. Herein, the pulse duration of the transmission pulses are set to be not shorter than a processing time period for receiving the electric waves while changing the direction of the receiving beam of the detector 10 over all azimuth angles in detecting the maximum received signal strength. A controller 35 of the detector 10 detects the rise of the transmission pulses and detects the electric wave arrival direction by receiving the electric waves while changing the direction of receiving beam of a detecting device over all azimuth angles since a detection point, in detecting the maximum received signal strength.