and extends into the filter unit 20 the driving unit 30 has a front and a rear output shaft not shown the rear output shaft extends into the smaller chamber 112 via the axle hole 141 of the positioning plate 14 the suction unit 40 is provided in the smaller chamber 112 and has a fan blade 41 rotatably driven by the rear output shaft of the driving unit 30 the blowing unit 50 is provided inside the filter unit 20 and has a fan blade 51 rotatably driven by the front output shaft of the driving unit 30 the blowing unit 50 is further provided with a downwardly oriented air outlet 52 the air outlet 52 is substantially cone shaped and has an elongated mouth which extends in the axial direction of the filter unit 20 the operation of the first preferred embodiment is as follows when the driving unit 70 is activated the sprocket 71 rotatably drives the chain 80 to cause axial rotation of the filter units 20 the filter units 20 are rotatably supported on the mounting plate 12 by the flange 211 of the filter units 20 which extends into the peripheral groove 61 of the bearing members 60 when the driving unit 70 is activated the driving units 30 inside the filter units 20 are simultaneously activated the output shafts of the driving unit 30 rotate.