PURPOSE: To prevent the fatigue breakage by thermally deforming a thermally deformed member according to the temperature of a working fluid and opening and closing an air discharge passage by a sealing part installed at the top edge part of the thermally deformed member, thus reducing the turbulence of the main flow in the vicinity of the air discharge passage and suppressing the vibrating force of a blade.

CONSTITUTION: Movable vanes 2 are arranged on the outer peripheral surface of a rotor 1, and static vanes 4 are arranged on the upstream side of the movable vane 2, on the inner surface of a casing 3 having the rotor 1 built in. Further, on the outer peripheral part in a prescribed stage drop part of the casing 3, an air discharge chamber 6 is formed, and communicates to the part between the movable vane 2 and the static vane 4 through an air discharge passage 7. With such constitution, a closing device 12 for the air discharge passage 7 is installed onto the inner surface of the casing 3. In other words, two thermally deformed plates 13a and 13b having different linear expansion coefficient are superposed by setting the plate having the larger linear expansion coefficient inside in the radial direction of the casing 3. Then, a sealing part 14 which closes the inlet part of the air discharge passage 7 is fixed at the top edge part of the thermally deforming member 13.