A thrust transmitting plate 14b on a cylinder hole bottom side portion of an adjuster nut 14, a drive side cam plate 12, and a cam spring 15 for biasing the thrust transmitting plate 14b toward the drive side cam plate 12 are accommodated in a generally cylindrical housing 16. Parts of the arc face of the circumferential wall of the housing 16 are deformed inwardly to form flat portions 16d. Engaging apertures 16e are formed in the flat portions 16d such that the engaging protrusions 14d are movable only in the cylinder axis direction when they are engaged. Portions of the circumferential wall of the housing 16 are protruded outwardly in convex shapes by presswork to form plural locking parts 16g arranged in the circumferential direction. The housing 16 is configured so as to be mounted in a cylinder hole 8 by latching those locking parts 16g to a circumferential groove 8f formed in the cylinder hole 8.