PURPOSE: To solve a reduction in performance so as to be suitable, particularly, for exhaust and compressing treatment of gas in which the deposition or sticking of a material is predicted by preventing the counter flow of air flow.

CONSTITUTION: A hollow annular housing 16 having an inlet port and a discharge port, and a ring guide core 14 arranged in the housing 16 are provided. An impeller 4 having a number of blades 13, 13,... for compressing the gas sucked to a main passage 15 formed by the outer circumferential surface of the guide core 14 and the inner circumferential surface of the housing 16 from the inlet port to the discharge port while transferring it is also provided. The top edge 21 of the blades 13, 13,... is formed into an inclined surface in which the outer diameter of the front edge on gas inlet side is smaller than the outer diameter of the rear edge on gas outlet side. Further, the opposed surface 19 to the top edge 21 of the blades 13, 13,... is formed into an inclined surface corresponding to the top edge 21.