To prevent valve handles from being erroneously operated because anyone can operate the handles which are exposed for operating the valves mounted around a facility.

A box-like cover which can contain the whole valve handle is cut into halves in the diameter direction of the valve. The two boxes of cut shape are mounted with a hinge on one of the sides corresponding to the valve handle thickness. The attachment method is implemented by expanding the valve handle through the action of the hinge for coverage from above and below and right and left sides when viewed from the direction in which the valve handle is rotated right to left. Then, the box-like cover divided into two halves spins free irrespective of the handle. Also, the two box-like halves are each provided with a keyhole, so that they are locked with a key to each other using the keyholes. In addition, the box-like cover cannot easily be rotated with a brute force because a palm is prevented from simply being brought into close contact with the cover due to the keyholes positioned in the center. As seen from the above, only a manager who locks the cover can operate the handle, resulting in the prevention of the erroneous operation.