Abstract: Provided is a device mounted on one end of valve body, remote from a manipulation lever attached to the other end of the spool, for retaining the spool at an offset position other than a position to which the spool is returned by the force of a return spring, wherein a shaft coaxial with the spool is formed directly therein with a linear guide section, a ring-like projection and a detent section, thereby the spool is retained not by pushing out balls in the direction radial from the axis of the spool, that is in the direction toward the inner wall of a casing, but by dropping the balls in the centripetal direction, that is, the direction toward the axis of the spool.