Abstract: A die set for bending a metal plate workpiece includes a lower die for placing the workpiece, an upper die having a pressing surface which presses the workpiece toward the lower die by movement, a lower movable part provided in the lower die and being slidable in the same direction as the direction of the upper die movement, and a gas spring elastically supporting the lower movable part from below. The pressing surface of the upper die is moved, contacts with the upper surface of the workpiece and presses the workpiece toward the lower die. The lower movable part being elastically supported by the gas spring from below brings an opposing surface into contact with the lower surface of the workpiece and makes the upper die to be close to the lower die while applying force in the upward which is opposite direction of the upper die movement.