An optical filter is provided on photoelectric conversion elements for monochrome reading. Each of a reflecting optical system and the optical filter has an end portion and a central portion in a predetermined direction. The optical filter suppresses light at a peak wavelength of a light source such that a difference between a sensitivity of optical path via the end portion of the reflecting optical system and the optical filter and a sensitivity of optical path via the central portion of the reflecting optical system and the optical filter fall within a range of 5% at the peak wavelength of light source.