PURPOSE: To permit the cleaning work of an insect screening simply and quickly by a method wherein a comb type brush, supported rotatably so as to be neighbored to the insect screening in parallel to the surface of the same substantially, is provided and a rotation driving member, connected to the brush, is operated.

CONSTITUTION: A ventilating duct 14 is extended to the inside of a building so as to be neighbored to a vent cap 12 projected out of the outer wall 60 of the building. A metallic insect screening 16 is fixed to the outside terminal of the ventilating duct 14 through the technique of spot welding and the like. A comb type brush 20 is arranged so as to be neighbored to the insect screening 16 in parallel to the surface of the same substantially. When the insect screening 16 is to be cleaned, the lid 36 of an inspection port 34 is removed and the terminal of a cable 22 is drain out of the inspection port 34, then, the inside core of the cable 22 is turned manually by gripping a grip 24 whereby the brush 20 is turned to contact it with the insect screening 16 and dust can be scraped down by the brush 20.