To prevent fires and fatal accidents by catching scattered flame cutting sparks, flame cutting slag or the like in a heat resisting sack, and further, to improve the operability of the cover by securing the latitude of an installing method on installing the sack, and the opening area of the sack and the latitude of its opening angles on the installation.

The cover consists of a frame part 16 and a heat resisting sack 17 provided on the frame part 16. The frame part 16 has a bent mechanism 20 the whole of which is bent to a V shape from a horizontal state. The heat resisting sack 17 is fitted to the frame part 16 so that the frame part 16 passes through the vicinity of the opening thereof so as to freely be slid. Further, both or either of a magnet 21 for adsorption and a hanging material is attached to the frame part 16 as a locking means.