PURPOSE: To prevent change and slippage of valve opening by providing an adaptor fixed on the edge part of a valve rod and a handle which can be connected to and disconnected from the adaptor by means of moving the valve rod upward and downward in the axial direction.

CONSTITUTION: A square part in the neighbourhood of the edge part of a valve rod l is engaged on the inner peripheral surface of an adaptor 2. Additionally, a handle 3 is connected to and disconnected from the adaptor 2 when it is moved upward and downward in the axial direction on the outer peripheral surface. At the time of installation of the handle 3, the valve rod l rotates by the rotation of the handle 3 and valve opening is changed. After this manual operation is finished, the handle 3 is disconnected from the adaptor 2, and therefore, even when an external force affects on the handle 3 by mistake, the valve rod l rotates and there is no worry about the change of valve opening.