A housing is made sealable even when the rigidity of a frame member and a cover member is not high. In an EFEM, a pressure difference having a predetermined value or less exists between an internal space of a housing and an external space of the housing. The housing includes a frame member assembled so as to form an opening, a cover member attached to the frame member so as to cover the opening, and a seal member sandwiched between the frame member and the cover member and configured to extend so as to surround the opening. The frame member and the cover member are formed of a sheet metal. The seal member is an elastic member having a hollow cross section orthogonal to an extension direction of the seal member.