An exposure apparatus projects a pattern of an original onto a substrate by a projection optical system to expose the substrate, wherein the projection optical system includes a mirror assembly, and the mirror assembly includes a first mirror member which has a first reflecting surface and is configured to bend an optical axis of the projection optical system, a second mirror member which has a second reflecting surface and is configured to bend the optical axis, a supporting mechanism configured to support the first mirror member and the second mirror member, and the supporting mechanism is positioned to position the first mirror member and the second mirror member while a positional relationship between the first mirror member and the second mirror member is maintained.