PURPOSE: To improve the reliability and responsiveness through the prevention of occurrence of runout in high speed rotation by supporting variable function bearings capable of operating to rotatably support a shaft through a controller at above a specified rotation of the shaft.

CONSTITUTION: No.1 ring-shaped bearing member 23 having a tapered surface 22 which becomes a bearing forming surface is rigidly fixed on a shaft 6 which is rotatably supported through a pair of bearings 5. On the other hand, No.2 ring-shaped bearing member 25 having a tapered surface 24 capable of abutting on the tapered surface 22 to become a bearing forming surface and capable of shifting in an axial direction is installed in a housing 26, and the tapered surfaces 22, 24 are abutted with the supply of oil from an oil passage 29, resisting against a return spring 37. When the shaft 6 exceeds a specified rotation, oil is supplied by a rotation sensor 33 and a controller 10, so that the shaft 6, supported by three bearings at high speed rotation, is prevented from causing runout to improve its reliability and responsiveness.