Spherical members 7 are provided between plural pairs of axial grooves 3, 5 which are respectively formed on the outer peripheral surface of a male shaft 1 and on the inner peripheral surface of a female shaft 2, a leaf spring 9 for preload is interposed between the axial groove of the male shaft and the spherical member, and columnar members 8 are provided between another plural pairs of axial grooves 4, 6 which are respectively formed on the outer peripheral surface of the male shaft 1 and on the inner peripheral surface of the female shaft 2. Moreover, the radius of curvature of a transverse cross section of the axial groove 5 on the side of the female shaft 2 in which the spherical member 7 is rotated is set as 55% or less of the diameter of the spherical member 7.