PURPOSE: To suppress the self-induced vibration of a rotary shaft for a stable rotation by a mechanism wherein at least one of clearances, formed between the inner sliding perimeter surface and the outer sliding perimeter surface of a floating metal in a cross section of a rotary shaft cut with a plane at a right angle thereto, takes a shape comprising plural gradual shrinkages and build-ups and an oil feed hole is set at a position having the largest clearance.

CONSTITUTION: Oil feed holes 2a and 3a are formed in a floating metal 2 and a bearing wheel chamber 3, and the inner perimeters of the floating metal 2 and the bearing wheel chamber 3 having radius R1 and radius R2 respectively are formed with respective sets consisting of three are surfaces. In so doing, a first sliding clearance 12 and a second sliding clearance 13, which lie between the outer perimeter of a turbine shaft 1 and the inner perimeter of the floating metal 2 as well as between the outer perimeter of the floating metal 2 and the inner perimeter of the bearing wheel chamber 3,. respectively, take shapes comprising plural gradual shrinkages and build-ups. And, the oil feed holes 2a 3a are set at the positions having the largest clearance at the clearances 12 and 13. Therefore, the thickness of the oil film always takes the shape of a wedge, and this fact suppresses the self-induced vibration of the turbine shaft 1 for a stable rotation.