An exposure apparatus for exposing a substrate to exposure light via an original. The apparatus includes a reflector, which includes a multilayer film and a ruthenium film, and reflects the exposure light. The multilayer film reflects the exposure light, and the ruthenium film is arranged on the multilayer film. A vacuum container contains the reflector, an exhauster exhausts exhaust gas in the vacuum container, and a regulator supplies water vapor into the vacuum container and regulates an amount of the water vapor in the vacuum container, based on an amount of carbonaceous gas in the vacuum chamber, so as to retard oxidation of the ruthenium film.