PURPOSE: To demonstrate a performance which is equivalent to a two stage oil separation system comprising a cyclone-type oil separator and a filter-type oil separator with one oil separator.

CONSTITUTION: A cylindrical member 16 whose lower end is open is extended downward, penetrating the central upper part of an enclosed vessel 51. A gas inlet pipe 43, which allows gas to flow in the tangential direction with the inner peripheral surface, is installed to the upper part of the cylinder-shaped member 46. A filter 55, which comprises a micro-fiber or the like so as to catch oil mist, is installed around the cylinder-shaped member 46 and at the same time, a gas outlet is installed to the upper peripheral edge of the enclosed vessel 51 while an oil outlet is installed to the lower part of the vessel.