A coned disc spring is arranged between a second component and a third component provided inside a tubular first component and movable in an axial direction. The coned disc spring comprises a body having a circular dish shape, teeth closely fitting into spline grooves formed on an inner peripheral surface of the first component and projecting to a radial outer side on an outer periphery of the body, and a stress relaxation portion formed by notching a base of the tooth in an approximately circular arc shape in a direction at least one of a circumferential direction and a radial direction of the body.