To prevent occurrence of contact of a fixed side and a rotational side in a sealing device for a rotational body such as a steam turbine by improving sealability while reducing a seal clearance in a normal operation area, and keeping a clearance sufficient for characteristic value speed in a resonance area.

A labyrinth member 7 as a seal member is slidably arranged on a rotor 3 as a rotational body in a radial direction. A plate spring 12 pressurizes the labyrinth member 7 toward the center of the rotor 3 against centrifugal force. A base of the labyrinth member 7 can be abutted against a packing housing 13 for regulating a radial direction position of the member 7.