Tapered coupling structure and rotating machine

A tapered coupling structure comprising:

• a tapered shaft having a taper part with a front end surface;
• and
• a hub to be coupled to the tapered shaft, wherein
• the taper part is on a side of the tapered shaft which is coupled to the hub,
• the hub includes a base part and a part having a thickness in a radial direction that is greater than that of the base part and having a rigidity in the radial direction that is greater than that of the base part,
• an outer peripheral surface of the taper part or an inner peripheral surface of the hub has formed therein a first oil groove, a second oil groove, and a connecting oil groove that communicates with the first and second oil grooves to feed oil to coupling surfaces of the taper part of the tapered shaft and the part and base part of the hub,
• the first oil groove is provided in a first region corresponding to the part of the hub in an axial direction,
• the tapered shaft has an axial oil passage located therein that extends in an axial direction of the tapered shaft from the front end surface of the taper part, and a radial oil passage extending in a radial direction of the tapered shaft and communicating with the axial oil passage,
• the radial oil passage has opposite ends that both open to the outer peripheral surface of the taper part, and
• the second oil groove is provided in a second region that is different from the first region and that is at a position at which the opposite ends of the radial oil passage open to the outer peripheral surface of the taper part.