To implement a prescribed detent function by a simple assembling work.

An internal circumferential side member 1 coaxially formed in a shaft center part of an outer circumferential shaft member 2 is provided with a plurality of vertical grooves 1b at equal intervals circumferentially, while the outer circumferential shaft member 2 is provided with steel balls 11 stored in a lateral hole 2a formed in the internal circumferential side of the outer circumferential shaft member 2 and connected to the vertical grooves 1b. The steel ball 11 is retained in a prescribed position by a curved plate spring member 14 stored in an annular groove 2b formed in the outer circumferential side of the outer circumferential shaft member 2 and energized toward the vertical grooves 1b.