PURPOSE: To provide the noise reduction method of an infrared image pickup device suitable for miniaturization.

CONSTITUTION: With respect to the infrared image pickup device, an aperture stop 3 determined by the exit pupil, a telecentric optical system 6 which emits the output light of the aperture stop 3 at the same solid angle, and a detecting element 9 provided in the incidence position of light from the telecentric optical system 6 are stored in a constant-temperature area 12. Thus, the noise is reduced, and the telecentric optical system is used to correct the variance in sensitivity of elements based on the change of the angle of incidence.