PURPOSE: To improve pressure characteristics and efficiency by providing a fluid blowing means for blowing off high pressure fluid in the direction so as to promote scroll formation of the fluid flowing into a main passage from an inlet port.

CONSTITUTION: In a housing 2 which forms a main passage 24, a blow-off passage 8 as a a fluid blowing means is formed. This blow-off passage 8 is formed by an introduction part 81, a guide part 82 and a blow-off part 83. A part of high pressure fluid in the main passage 24 is introduced to the neighborhood of an inlet port 61 by the blow off passage 8. The fluid flowing into the main passage 24 from the inlet port 61 directly flows into a blade and blows off in the direction to promote formation of a scroll. Thus, the scroll is formed in the main passage 24 without disturbing flow of the fluid near the inlet port 61. Therefore, pressure characteristics and efficiency can be improved.