To provide an illumination optical apparatus which can adjust the position of an illumination area formed on an illuminated face while at the same time suppressing a loss of optical energy.

The illumination optical apparatus illuminates the illuminated face (M) based on the luminous flux from a light source (1). The apparatus comprises an optical integrator (7) which is located in an optical path between the light source 1 and the illuminated face and forms a secondary light source based on the luminous flux from the light source 1, and an optical guide optical system (9, 10, 11) which is located in an optical path between the optical integrator and the illuminated face and guides the luminous flux from the secondary light source to the illuminated face. The optical guide optical system includes a reflection mirror (M2) which is so structured as to make a fine movement in order to adjust the position of the illumination area to be formed on the illuminated face. By making a fine movement of the reflection mirror located in an optical path of the optical guide optical system, the position of the illumination area to be formed on the illuminate face can be adjusted. Unlike the conventional technology where the position of the illumination area is adjusted by moving a field stop, this new method goes substantially without a loss of optical energy in the field stop. Consequently, the position of the illumination area to be formed on the illuminated face can be adjusted while at the same time sufficiently suppressing a loss of optical energy.