An exposure apparatus for exposing a substrate to ultraviolet light via a pattern of a reticle. The apparatus includes an optical element disposed on a path of the ultraviolet light extending from a light source to the substrate, a holder configured to hold the optical element, and a container configured to accommodate the optical element therein. The container has a partition wall with an opening through which the holder extends. The partition wall and the holder have a gap therebetween inside the opening. The holder is configured to move in a range of the opening so as to adjust a position of the optical element. The partition wall and the holder is configured so that a portion of the gap can be filled with a detachable filling cover. The apparatus further includes an outer cover detachably mounted on the container to cover the partition wall gas-tightly, and a supplier configured to supply inert gas into the container.