An exposure apparatus for exposing a substrate to light via an original plate. A projection optical system projects a pattern of the original plate onto the substrate, a liquid immersion mechanism generates a liquid immersion state in which a gap between the final surface of the projection optical system and the substrate is filled with liquid, a first photosensor detects light which has passed through the projection optical system, a second photosensor, different from the first photosensor, detects light that has passed through the projection optical system, and a controller calibrates an output from the first photosensor in the liquid immersion state based on a first output from the first photosensor in the liquid immersion state, a second output from the first photosensor in a non-liquid immersion state, and a third output from a reference illuminometer.