To easily apply grease to a shaft end part internal peripheral spline.

In the case that a spline 9 is formed in the internal periphery of a hollow shaft end part 1a, this method applies grease G to this spline, a cap 60 is insertion fitted to the internal/external peripheral side of this shaft end part, the cap, provided with an outer cylinder part 61 fitted to the external peripheral side of the shaft end part, an inner cylinder part 62 positioned inside this outer cylinder part to be fitted to the internal peripheral side of the spline to be protruded in the cap insertion direction relating to the outer cylinder part, and a connection part 63 connecting these inner/outer cylinder parts on this side of the cap insertion direction, is prepared, after the grease G is applied to a protruded part external peripheral surface 67a in the inner cylinder part of this cap, by inserting the cap 60, the grease applied to this protruded part external peripheral surface is made to adhere to the spline 9.