To jet stable, strong and uniform air, by keeping a constant width of an air discharge port, without locally expanding the air discharge port formed in an air supply chamber and opened in a slit shape, by internal pressure of the air supply chamber.

An air discharge ports 16 of two rows are arranged in a zigzag shape, and a first air suction port 26 and a second air suction port 27 are arranged in a zigzag shape on its outside so as to become a step difference shape. High speed air vertically injected toward a plate P from the air discharge port 16, is sucked and removed from the first and second air suction ports 26 and 27 together with dust after separating the dust stuck to the plate P by its wind pressure. The air discharge port 16 formed in the air supply chamber 11 and the first and second air suction ports 26 and 27 are respectively arranged in a zigzag shape, so that a constant width-keeping state can be maintained without locally expanding or narrowing the air discharge port 16 or the first and second air suction ports 26 and 27 by pressure.