To provide a turbine constantly maintaining a proper clearance between a rotor blade and a shroud during an operation period, and having a long durable period even under high temperature and easy repairing and reclamation.

A tip of the rotating rotor blade is used as a face 14 to be ground, an inner wall of the shroud 20 comprising a mantle of the rotor blade is used as a grinding face 23, a part of fine particles of abrasive particles 13 protrudes from the face 14 to be ground, and protruding parts 13a of the abrasive particles slide against the grinding face 23 and are worn when the tip of the rotating rotor blade contacts the inner wall of the shroud 20.