To select and detect a flying body only as a target without detecting the gound or cloud.

An optical system 1 collects infrared rays of wavelength band containing the vicinity of 2.7μm and images them on an infrared detector 3. A narrow band filter 2 transmits an infrared band of center wavelength in the vicinity of 2.7μm. The infrared detector 3 generates detected signals by photo-electric transferring of infrared rays of wavelength band containing the vicinity of 2.7μm. A target extractor 6 selects a target from the detected signals. A tracking error computer 7 knows an angle between a visual line and a target position, and computes a tracking error quantity corresponding to it. A visual line controller 9 controls to drive a visual line control mechanism 8 so as to scan and orient the visual line. A target angle gauge 10 addingly processes the angular position of the visual line obtained by the visual line control mechanism 8 and the angle between the visual line obtained by the tracking error computer 7 and the target position, so as to obtain the relative angle of the target in an inertia space.