dropping the transport object onto the connection part 200 furthermore the dust kicked up in the connection part 200 is blown off from the conveying port together with air and glided into the dustproof box 300 since a sectional area of the dustproof box 300 is sufficiently large a flow speed of air containing the dust is remarkably decreased and dusts having large sizes are dropped on the transport object w disposed on the conveyer belt 100 by their own weights due to decrease of the flow speed meanwhile dusts having large sizes which are not dropped by their own weights first collide to a first mesh plate 330 and some of them are dropped on the transport object w disposed on the conveyer belt 100 and the remainder is adhered to the mesh plate 330 the dusts having small sizes which have passed through the first mesh plate 330 are decreased in a flow speed and the dusts are dropped by their own weights on the transport object w disposed on the conveyer belt 100 meanwhile dusts having large sizes which are not dropped by their own weight collide to a second mesh plate 330 and some of them are dropped on the transport object w disposed on the conveyer belt 100 and the remainder is adhered to the mesh plate 330 in this manner air containing dust is.