To drastically improve workability at the time of replacement of an inlet side filter without detaching an air introducing pipe from a suction port or even if the air introducing pipe is arranged in close vicinity to the wall of a building, or the like.

The planar inlet side filter 13 for first capturing oil mist is housed in a filter cage 10 capable of being laterally taken in and out along guide rails 15 and 15 provided to a filter case 3B. A collision plate 17 is attached to the center part at the front of the filter cage 10, and a dust receiver 18 for housing dust fallen off by the collision plate 17 is protruded forwardly to be integrally provided to the filter cage 10. A side cover for covering the taking in and out part of the filter cage 10 integrated with the collision plate 17 is provided to the side surface of the filter case 3B and, if the side cover is detached, the filter can be simply replaced. The dust receiver 18 is integrated with the filter cage 10 and the mixing of a cutting powder or the like, with collected oil can be reduced to the utmost.