A handle 13 is formed in a hollow shape. A displacement sensor 4 is fixed to an inner surface of the handle 13. The target 5 includes: a target body 22 which is arranged at a position away from a valve stem by a predetermined distance in the handle 13; a detection-use inclined surface 23 which is formed on a surface of the target body 22 which faces the displacement sensor 4 in an opposed manner; and a downwardly projecting portion 25 which projects downward from the target body 22. A lower surface of the downwardly projecting portion 25 of the target 5 is received by a valve body 11b so that the target 5 is rotated together with the handle 13 but is not upwardly and downwardly moved with respect to the valve body 11b.