1. A shaft device comprising:a nut support, a spline shaft, a shaft hole, a spline nut, a thrust bearing, and a return spring;
the spline nut having a tubular shape, being disposed coaxially with a portion of the spline shaft protruding upward from the shaft hole;
the thrust bearing rotatably supporting the spline nut in a housing portion, wherein the thrust bearing further comprising:
a shaft-side track plate being in contact with an end of the spline nut;
a housing-side track plate being composed of a bottom wall of the housing portion; and
a rolling element locating between the shaft-side track plate and the housing-side track plate
the return spring being configured to bias the thrust bearing in an axial direction of the spline shaft, wherein
the nut support including the housing portion housing an end portion of the spline nut.