Provided is an infrared image sensor for detecting infrared rays. The infrared image sensor includes a light-receiving unit including a pixel region in which a plurality of pixels are arranged and at least one reference pixel; a difference circuit for acquiring a first differential signal that is a differential signal between a signal of one pixel contained in the pixel region and a signal of the reference pixel and a second differential signal that is a differential signal between signals of two predetermined pixels out of the pixels contained in the pixel region; and a pixel signal calculating unit that calculates a signal of each of the pixels on the basis of the first differential signal and the second differential signal.