There is disclosed a illumination optical apparatus for illuminating a second surface optically conjugate with a first surface via a reflection type original plate which can be arranged on the first surface, the illumination optical apparatus comprising: a first partial field stop arranged to define a first outer edge of a illumination region which is to be formed on the second surface, in order to limit a light beam traveling toward the first surface; and a second partial field stop arranged to define a second outer edge of the illumination region, in order to limit a light beam reflecting from the reflection type original plate which can be arranged on the first surface, wherein a first distance between the first partial field stop and the first surface is set to be larger than a second distance between the second partial field stop and the first surface.