There is provided an illumination apparatus including an optical integrator including multiple optical systems for receiving light from a light source, and for producing multiple beams for illuminating a plane of mask or reticle on which a pattern is draw, a position of an incidence plane of the optical integrator and a position of the plane to be illuminated being arranged optically conjugate with each other, and a device for forming an optical characteristic distribution of light at the incidence plane, the light entering at least part of the multiple optical systems, whereby different areas on the plane of plane to be illuminated can be illuminated under different illumination conditions.