An exposure apparatus comprises an illumination optical system configured to illuminate a reticle with a light beam from a light source, a projection optical system configured to project a pattern of the reticle onto a substrate, a measurement unit configured to measure a light quantity distribution in an exposure area on an image plane of the projection optical system, and a detection unit configured to detect an existence of a foreign particle in the illumination optical system and the projection optical system based on the light quantity distribution measured by the measurement unit.