The present invention provides an optical element which is used for light having a wavelength not more than 250 nm, and receives a light beam at a maximum incident angle not less than 55°, wherein the optical element includes an optical thin film in an effective aperture thereof, and a film thickness distribution of the optical thin film in the effective aperture includes a distribution in which a thickness of the optical thin film in an outermost periphery of the effective aperture is 1.10 times (inclusive) to 1.25 times (inclusive) a thickness of the optical thin film at a midpoint between an optical axis and the outermost periphery of the effective aperture.