unit 1 the reference numeral 16 represents a cradle cover that can be opened upward the air current rectifier plate 13 in this embodiment is rotatable around the nozzle tip 1a and devised so that the bottom edge of the cradle cover 16 is brought into contact when completely closed with a cutout step 14 of the rectifier plate 13 closing cradle cover 16 thereby rotates plate 13 into a position in which the cutout 11 for the air flowing from said first nozzle 5 communicates with the air flow path 17 also in the above embodiment as the rectifier plate 13 is provided with a step 14 at the upper part 13a thereof and is in the shape of a disk capable of rotating freely in the dust box 3 it can be automatically put into the correct position by closing the cradle cover whereby great convenience is provided for cleaning the interior of the dust box 3 the rear face 21 of said lower half part 13b of the plate 13 is brought into contact with the front face of the nozzle holder 10 which serves as a stopper since the air current in the dust box 3 is rectified by provision of such rectifier plate 13 as above the opening 22 on the bottom of the dust box 3 is enabled to be wider and in the form of a single opening rather than the two openings 23 and 24 in the dust box 3 shown in fig1 in the present invention the air flow path to the dust box 3 is partitioned into a path 20 for the sucked air current on the nozzle tip side and another path 17 for the discharged air current from the first nozzle 5 therefore fly waste and.