An endoscope system includes: an image acquiring unit that acquires a first frame image obtained by photographing a photographic subject and a second frame image obtained by photographing the photographic subject at a timing different from that of the first frame image; an oxygen saturation calculating unit that calculates an oxygen saturation by using the first frame image and the second frame image; a reliability calculating unit that calculates reliability of the oxygen saturation, calculated by the oxygen calculating unit, by using a signal ratio that is a ratio between a pixel value in a first specific wavelength range corresponding to a specific wavelength range of the first frame image and a pixel value in a second specific wavelength range corresponding to the specific wavelength range of the second frame image; and an information amount adjusting unit that adjusts an information amount of the oxygen saturation by using the reliability.