An enclosure for an imaging device. In one embodiment, the enclosure includes a housing with a transparent window. A shutter mechanism is disposed on the housing and transparent window, and includes an opening formed therein. A shutter covers and uncovers the opening. Further, a gas supplying unit supplies gas to a space between the housing and the shutter mechanism. In another embodiment, the enclosure includes an inner housing with a transparent window, and an outer housing overlapping the inner housing and with an opening formed therein. A driving unit moves the opening along a predetermined path over the transparent window. A gas supplying unit supplies gas to the outer. In yet another embodiment, the enclosure includes inner and outer housings each having an opening formed therein. A rotating unit rotates one of the inner and outer housings, and a gas supplying unit supplies gas to the inner housing.