To form an attachment part of a support member attached for supporting a metal box without allowing the interior of the box to communicate with the exterior of the box.

A metal box has an opening at one side, is formed into a box shape with a closed bottom, and is supported by support members fixed to a construction. The metal box includes a tubular peripheral wall and a bottom wall facing the opening. Cut-and-raised parts, each of which is cut and raised toward the exterior part of the peripheral wall and has an attachment part for attaching the support member, are provided on the peripheral wall. Communication areas between the interior and the exterior of the peripheral wall which are made by cutting and raising the cut-and-raised parts are respectively closed by closing pieces folded along areas ranging from an opening end of the peripheral wall to an inner surface of the peripheral wall.