A sleeve has a female thread, which is formed in an inner peripheral surface of the sleeve. An adjust screw adjusts a spring load of a spring, which is placed in an inside of the sleeve. The adjust screw has a male thread, which is formed in an outer peripheral surface of the adjust screw and is threadably engaged with the female thread. The sleeve has at least one protrusion that is formed integrally with the rest of the sleeve and is urged against the adjust screw toward the spring in an axial direction to urge the male thread against the female thread and thereby to provide a predetermined degree of sealing between the male thread and the female thread.