An illumination optical apparatus illuminates a pattern on a mask with illumination light. The illumination optical apparatus includes an optical integrator arranged in an optical path of the illumination light, a deflecting member arranged in the optical path on an incidence side of the optical integrator, which deflects the illumination light, a lens element arranged in the optical path between the deflecting member and the optical integrator, which distributes the illumination light in a region, on a pupil plane of the illumination optical apparatus, away from an optical axis of the illumination optical apparatus, and a polarization member arranged in the optical path between the lens element and the optical integrator, which changes a polarization state of the illumination light so that a polarization direction of the illumination light in the region is substantially coincident with a circumferential direction about the optical axis.