PURPOSE: To make it possible to rotate a disk at a super high speed, by coupling the conical protruded part of a shaft with a cone shaped tapered hole which is provided in a turbine disk, and holding the disk by the surface pressure of the tapered hole.

CONSTITUTION: A cone shaped tapered hole 13 is formed at an inner hole 14 of a turbine disk 1. A conical protruded part 12, which is coupled with said tapered hole 13, is provided at a shaft 2. A bush 3 is provided at the other part of the shaft 2. The bush is tightened by a nut 5 through a coned disk spring 4 and a spherical washer 6. Thus the disk 1 is held by the surface pressure of the tapered hole 13. Even though the disk 1 is rotated and the inner hole 14 becomes large due to a centrifugal force, the protruded part 12 is pushed into the hole 13 by the elasticity of the coned disk spring 4, and the disk 1 is held to the shaft 2. Therefore vibration due to unbalance is not yielded, the disk 1 can be rotated at a high speed of 5,000W20,000 rotations, and residual stress can be added.