To improve so as not to cause a hitch on a spline shaft at its inlet end by arranging a carbon fiber dispersed resin layer forming a screw thread on an inside surface, and installing ceramic hollow cylindrical members in gateways on both ends.

Installing parts 107 and 108 having a diameter larger than an inside diameter 106 of an outside part 105, are respectively formed in a range of a prescribed length from a flange part side end surface 104 and the other end surface 103 of the outside part 105 of a spline nut 1 where a carbon fiber dispersed resin 101 layer is arranged on an inside surface, and ceramic parts 5 and 6 are fitted in them, and are fixed by an adhesive. This is screw- fitted to a spline shaft 2, and the spline shaft 2 is reciprocally rotated, and the spline nut 1 is sent in the reciprocal direction along the spline shaft 2. In that case, since inside surfaces of the ceramic parts 5 and 6 which are arranged in gateways of the spline snut 1 and have high hardness and strength and are excellent in a balance of these move by contacting with a screw thread of an outer peripheral surface of the spline shaft 2, a hitch is not caused.