To reasonably increase fastening force to a guiding member, by interposing plural balls between inner and outer rings, and forming the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring into a tapered surface, wherein one-end sides in axis directions become large diameters respectively.

Reaction force receiving members 41 and 51 are made to abut on one end in the axis direction of an inner ring 100, also pistons 40 and 50 are made to abut on the other end in the axis direction of an outer ring 101, and moreover the outer peripheral surface of the inner ring 100 and the inner peripheral suface of the outer ring 101 are formed into a tapered surface, where one-end sides in an axis directions become large diameters respectively. When the inner and outer rings 100 and 101 are nippedly pressed in the axis direction between the reaction force receiving members 41 and 51 by pressing force of the pistons 40 and 50, a ball 102 is pushed in an inner part in a diameter direction by the wedge action of the tapered surface, to reduce the diameter of the inner ring 100 to fasten a guiding member (b).