To detune a turbine impeller 33 in a specific high speed zone by simple additional work and simple design change, and to avoid the resonance of the turbine impeller 33.
A notch 61 is formed at a part of an outer edge of each turbine blade 37, and an orienting direction of a tip of each notch 61 is perpendicular to an axial center of a turbine impeller 33. A recessed part 63 is formed at an outer edge of each turbine blade 37 and each of the recessed part 63 includes a progressive reduction area 63a in which a length from an axis C of the turbine impeller 33 progressively decreases toward a downstream side, and a progressive increase area 63b which is adjacent to a downstream side of the progressive reduction area 63a and in which a length from the axis C of the turbine impeller 33 progressively increases toward a downstream side.
Iwa Saki Kokuni
Kawamata Sumio
Masakazu Ito
Shunichi Takahashi
Toshio Takamatsu