Coupling and method for fixing the same

A coupling comprising:

• a body member including a fitting hole into which an end of a spline shaft is fitted, and a connecting portion to which another member is mounted, the spline shaft including a plurality of spline grooves linearly extending in an axial direction at an interval in a circumferential direction;
• a positioning mechanism that positions the body member in the circumferential direction of the spline shaft with respect to the spline shaft fitted into the fitting hole of the body member;
• and
• a fixing portion that fixes, to the spline shaft, the body member in a state of being positioned by the positioning mechanism, wherein
• the positioning mechanism includes a screw hole provided in the body member so as to penetrate from an outer surface of the body member to an inner surface of the fitting hole along a radial direction, a screw member fastened into the screw hole, and a pressing part having a circular cross section, provided in a tip of the screw member, and pressed against the spline groove by fastening of the screw member into the screw hole.