PURPOSE: To prevent loosening of connection by fixing locking ring which is supported by the impeller and the liner ring with the multi number of convexed parts into which the inner peripheral fringe of the locking ring is bent.

CONSTITUTION: The locking ring 1 is inserted between the liner ring 2 and the impeller 3. The appropriate number of locking convexes 20, 30 are cut in the inner peripheral part of the liner ring 2 and the suction side end inner peripheral of the impeller 3 so that the inner peripheral of the ring 1 is bent into the convexed parts 20, 30. Since the outward bending piece 12 is engaged in the liner ring groove 20, the liner ring 2 and the locking ring 1 do not rotate. Also, as the inward bending piece 13 is engaged in the convex part 30 of the impeller, the relative rotation of the locking ring 1 and the impeller 3 can be prevented. Therefore, the rotation of the liner ring 2 relative to the impeller 3 is prevented.