Patent ID: 7719661

Claim:
A reflection type illumination optical apparatus which guides an illumination light to an illumination objective surface, the illumination optical apparatus comprising: an optical system including an optical integrator having a plurality of reflecting mirror elements, a first reflecting surface which reflects the illumination light reflected by each of the plurality of reflecting mirror elements, and a second reflecting surface which guides the illumination light reflected by the first reflecting surface to the illumination objective surface, the optical system defining a position conjugate with the illumination objective surface between the optical integrator and the illumination objective surface; and a partition wall member separating a first space in which the first reflecting surface is arranged and a second space in which the second reflecting surface is arranged into mutually different vacuum environments or pressure-reduced environments, the partition wall member having an aperture which is formed in the partition wall member and through which the illumination light passes; wherein the aperture of the partition wall member is arranged at a position at which a cross-sectional area of a light flux of the illumination light reflected by the first reflecting surface is smallest, or the aperture is arranged in the vicinity of the position.