PURPOSE: To moderate a concentration of stress produced at the point of installation of the casing, by dispersing a force, transmitted to a ring-shape main plate from the casing, to a side of outer ring-shape main plate through a reinforcement material.

CONSTITUTION: In a parallel type speed ring, a stay vane 2 is secured between an inner ring-shape main plate 4a and outer ring-shape main plate 4b, with a flow path constructed from a casing 3 to a guide vane (not shown in the drawing). To the peripheral part of the inner ring-shape main plate 4a, is secured an opening end of the casing 3, further in the peripheral side of the inner ring-shape main plate 4a, is arranged the outer ring-shape main plate 4b through the certain distance, and the outer ring-shape main plate 4b and the casing 3 are secured to each other by a plurality of reinforcement material 5. Accordingly, as the water flows from the casing side 3 to the stay vane side 2 through a ring-shape space between the inner ring- shape main plate 4a and the outer ring-shape main plate 4b, an ineffective sectional area of the casing 3 can be reduced resulting in a prevention of the concentration of stress.