PURPOSE: To uniformize the illuminance of the whole surface of a reticle and to maintain the NA of an illumination light to the reticle constant irrespective of its azimuth by disposing an image rotator between a light source and an integrator in an illumination optical system for a semiconductor exposure device, and rotating the rotator at an optical axis a center during exposure.

CONSTITUTION: A luminous flux irradiated from an excimer laser light source 1 is incident to an image rotator 8 rotated at an optical axis as a center, and rotated. After the flux is enlarged by a beam expander 2, it is irradiated to the edge face of an integrator 3. Accordingly, even if the section of the flux radiated from the source 1 has any illumination distribution, if the time average is taken at the face of the integrator 3, an illumination having symmetrical characteristic with respect to the optical axis is performed. On the other hand, if the illumination distribution of the incident edge face of the integrator 3 is axially symmetrical, the intensity distributions of a plurality of light source images formed near the radiating edge face of the integrator 3 become axially symmetrical. Accordingly, the illumination distribution of the entrance pupil of a projection lens becomes axially symmetrical, and the NA of the illumination light to a reticle 5 becomes constant irrespective of its azimuth.