PURPOSE: To prevent the blade of an impeller from interfering fluid flow by carrying fluid into the out of a machine from the external periphery of a main flow passage and changing the flow direction inside both a suction passage and a discharge passage.

CONSTITUTION: Both a suction passage 61 and a discharge passage 62, external openings 61a and 62a which are placed outside a main flow passage 24 and formed on the side face of a housing 2 perpendicular to a driving shaft 7 are communicated with internal openings 61d and 62d which are placed on the external periphery of the main passage 24 and formed on the plane approximately perpendicular to the plane on which the external openings 61a and 62a are formed. In addition, the sectional view of each of the suction passage 61 and the discharge passage 62 is rectangular. Fluid is rectified by the blades 32 before entering without interference so that the creation of interference noise may be prevented.