PURPOSE: To detect an object accurately by selecting an optimum filter in response to the state of the sun-ray so as to extract the energy from an object accurately without being affected of a change in the sun-ray.

CONSTITUTION: Output video data from an infrared ray solid-state image pickup element 2 when a test use short wavelength filter 3-1 is inserted to the device are inputted to a data processing section 5, in which an arithmetic mean of a pattern is obtained and an optimum filter corresponding to the mean value is selected among interruption short wavelength filters 3-2-3-n and the result is informed to a control section 4. Thus, the control section 4 controls the optimum filter to be inserted between an optical system 1 and an image pickup device 2. Thus, an object energy is obtained by suppressing the effect of the solar energy and an object is accurately detected.