PURPOSE: To provide a sufficient damping effect by giving torsional moments to one and the other of adjacent turbine moving blades fitted closely to each other alternately and reversely in the axial direction perpendicular to the outer periphery of a rotor wheel for assembly in sequence.

CONSTITUTION: Shrouds 4 are molded integrally with reference moving blades 1, shrouds 7 are molded integrally with adjacent moving blades 6, and they are fitted alternately into a rotor wheel for assembly. The front contact surface of the shrouds 4 of the reference rotor vanes 1 is inclined by an angle of θclockwise as viewed from the top of the moving blade relative to the back contact surface to form so that the outlet of the shroud 4 is slightly larger in width than the inlet of it. On the contrary to the reference moving blade 1, in the adjacent moving blade 6, the inlet width of the shroud 7 is formed larger than the outlet width of it. When the shrouds 4 and 7 are assembled with sufficient surface pressure provided, torsional moments M faced reversely to each other are produced and also moving blade effective part is twisted by an angle of θ/2. Thus a sufficient damping action due to Coulomb friction can be maintained against centrifugal force and wheel bulge during the turbine operation.