To thin the thickness of a casing without increasing the circulation resistance of a suction or discharge passage of an air cleaner.

A plate shaped filter 27A is mounted between a suction port or a discharge port and an outer plate 20 of the casing A, a space formed between the filter and the outer plate is used as at least a part of the suction or discharge passages C2, C2, B, and the air is introduced into the space from the direction in parallel with the outer plate. The filter is mounted in a state that a distance to the outer plate is gradually increased in accordance with the approach to an end edge at the neighborhood of the end edge 27A1 at a side to which the air is introduced. The filter may be a flat plate or a V-shaped plate. A partition 22 is mounted along a bent part of the filter to separate the space between the filter and the outer plate into two partial spaces, and two partial spaces may communicate to different air suction ports 12, 23.