PURPOSE: To directly cool an impeller with the outside air efficiently by providing a cooling opening communicated to a car room, and providing a radiator on a hub section arranged on the cooling opening.

CONSTITUTION: A cooling means provided on a fluid device is constituted of a cooling opening 20 communicated to a car room 6 and a radiator 21 provided on a hub section 5 arranged on the cooling opening 20, and the radiator 21 has a group of fan blades 21a of an impeller 1 arranged on the cooling opening 20. The impeller 1 is rotated together with a rotary shaft 3 in the operation state, and a fluid generating an eddy current in a main passage 8 is continuously pressurized by blades 7 of the impeller 1. Cooling air is sucked through an inlet opening 20a by the rotation of the fan blades 21a, it is pressurized and blown off to the outside below a housing 3 via an outlet opening, and the impeller 1 is directly cooled by the air stream generated by the fan blades 21a.