PURPOSE: To prevent snow which has made ingress into the device from adhering to the surface of the filter through an external air intake port by providing an eliminator between the external air intake port and the filter and also providing in the eliminator a flow-in nozzle from the external air intake port side.

CONSTITUTION: An eliminator 21 is formed by disposing V-shaped groove materials 21a opening on the side of a bag type-filter 4 and extending vertically in two zigzag rows. Snow or dust infiltrating into a space 20 together with external air adheres onto the surface of each V-shaped groove 21a or is sieved out and eliminated while passing through the eliminator 21, and hence snow does not adhere to the surface of the bag type filter 4. Snow or dust which has adhered to the surface of the eliminator 21 is melted by the sprinkling of water from the flowing water nozzle 22 and is turned out to be snow water and increased in the weight of water. The snow water flows down along the eliminator 21 and on the floor surface 26 of the space 20 and is arrested by a drain pit 27. Then, foreign matters are removed from the snow water by a strainer 28, and thereafter the snow water is sent to a non-radiation drain tank.