To surely lock a non-rotating member even when an installation space at a car body side is narrow and limited, and to prevent movement in the operating direction from being disturbed as much as possible in a state of locking the non-rotating member.

Engagement claws 23d, 23d and 30d, 30d each having the quarter cylindrical shape are projected from spring retainers 23, 30 supporting both ends of a return spring 31 in a state of being faced to each other. The phases of the spring retainers 23, 30 are shifted from one another by 90 degrees to alternately engage the engagement claws 23d, 23d and 30d, 30d of both spring retainers. Whereby the non-rotating member is locked.