Abstract: A first rotation limiting surface where a curvature is partially reduced in a circumferential direction is provided on an outer circumferential surface of an inner shaft fitting. A press-fit fitting is installed to the outer circumferential surface of the inner shaft fitting including the first rotation limiting surface. A second rotation limiting surface where a curvature is partially reduced in the circumferential direction corresponding to the first rotation limiting surface is provided on an inner circumferential surface of an insertion hole of the press-fit fitting. The first and second rotation limiting surfaces are mutually superimposed in a press-fit state. A press-fit guide surface located on a central side of the inner shaft fitting to the first rotation limiting surface and having a width dimension greater than the first rotation limiting surface is axially outer of the first rotation limiting surface on the outer circumferential surface of the inner shaft fitting.