To provide an illumination optics that facilitates forming a desired light intensity distribution having no illumination irregularities at a pupil position of the illumination optics or a position optically conjugated with the pupil position, even when the light from a light source includes unevenness of light intensity in the cross-section of light.

The illumination optics which illuminates an irradiated plane with illumination light provided from a light source 1 includes a spatial light modulator S1 which is arranged in an optical path of the illumination optics and cooperates with part of the illumination optics to form the desired light intensity distribution at the pupil position of the illumination optics or the position optically conjugated with the pupil position. The system includes light receiving surfaces 32a, 33a which receives some of the illumination light. Detection units 30-33 detect the light intensity distribution of the illumination light at a position in an optical path extending from the light source to the spatial light modulator. A control unit 20 controls the spatial light modulator based on the light intensity distribution of the illumination light detected by the detection unit.