An exposure apparatus includes an illumination optical system adapted to illuminate a reflection mask with light from an exposure light source, and a projection optical system adapted to project a pattern image of the reflection mask disposed in an object plane onto a substrate disposed in an image plane. The illumination optical system includes a reflection integrator adapted to form a plurality of secondary light sources with the light from the exposure light source, a condenser unit adapted to superimpose beams of light from the secondary light sources with one another on the reflection mask, and a mirror capable of being disposed in an optical path instead of the reflection integrator. When the mirror is disposed in the optical path, an illuminated area formed in the object plane of the projection optical system is reduced in comparison with that formed when the reflection integrator is disposed in the optical path.