An illumination optical apparatus, used in a projection exposure apparatus for projecting and exposing a pattern arranged in a first plane to a second plane, for supplying the first surface with illumination light from a light source comprises an optical path combiner arranged in an optical path between the light source and the first surface, for combining a plurality of light beams different from each other from the light source such that the first and second light beams illuminate the first surface closely to each other. The optical path combiner includes a discrete point positioned on or near a third surface optically conjugate with the first surface. The plurality of light beams travel by way of a plurality of regions sectioned by the discrete point, respectively.