Images are formed from first and second polarized images acquired through illumination of the subject with first illumination light beams, and third and fourth polarized images acquired through illumination of the subject with second illumination light beams. Images of a subject are formed from translated first, second, third, and fourth polarized images, acquired from first and second luminous point images. The first bright spots appear on the first polarized image when the first illumination light beams are mirror-reflected off the subject. The second bright spots appear on the fourth polarized image when the second illumination light beams are mirror-reflected off the subject. The image forming circuit forms images of the subject by calculating a difference between a first average image, obtained by averaging the translated first and fourth polarized images, and a second average image, obtained by averaging the translated second and third polarized images.