To detect degradation of an infrared detector by a simple and small constitution.

A first radiation plane 320 set to a first radiation ratio and a second radiation plane 330 set to a second radiation ratio different from the first radiation ratio are formed on a shutter 300. An arithmetic processing unit 520 calculates, on a pixel to pixel basis, a difference between the value of first imaging data obtained by imaging the first radiation plane 320 by an infrared detector 100 and the value of second imaging data obtained by imaging the second radiation plane 330 by the infrared detector 100. A determination unit 530 determines the sensitivity of the infrared detector 100 on the basis of the difference calculated by the arithmetic processing unit 520.