Abstract: A safety fence for a square hatched formed in a slab of a building is provided. The fence has lids pivotable about opposed sides of the hatch, and has such a size that about half of the opening of the hatch is closed by each of the lids. Side frames having a predetermined height are pivotable about opposed sides of the hatch. A plurality of gear mechanisms is provided, with each mechanism comprising a first gear and a second gear in mesh with each other, a first shaft supporting the first gear, a second shaft supporting the second gear, the first and second shafts extending parallel to the opposed ends of the hatch, the first gears being secured to lower ends of the lids, and counterweights mounted to one of the second shafts. The safety fence is set up by erecting the lids and the side frames. A plurality of brackets each having a pair of bracket portions secured to the inner wall of the hatch.