To provide a draft chamber capable of disposing a weight inside a side wall of a housing so that it doesn't interfere with pipelines or the like, and eaily replacing and inspecting of cords connecting the weight and a door.

This draft chamber is configured so that cords 12a, 12b fixed on both right and left sides of the door 11 are hung over a movable pulley 28 for hanging the weight W that moves vertically at an upper part inside one side wall 19 forming a hollow of the housing 10, and respective free ends of the cords 12a, 12b hung over the movable pulley 28 are fixed on the top of the housing 10.