PURPOSE: To prevent a travelling body from dust swirling up right above by providing a side wall surrounding the side of a gas layer formed between a travelling path and the travelling body while providing an exhaust path communicating to the gas layer.

CONSTITUTION: When air A is jetted from an air pallet 6 of a travelling bed 2, an air layer 10 is formed between the travelling bed 2 is brought to the floating-up condition. When the travelling bed 2 is energized by a liner motor 8 under such condition, said bed 2 travels in the desired direction to transfer a wafer 13. Said air A jetted from the air pallet 6 of the travelling bed 2 forms the air layer 10 between said bed 2 and guide table 1 and then is exhausted to be sucked into an exhaust path 11 opened to a side wall 9. Then, dust 15 on the guide table 1 is carried by the flow of air A, exhausted from the exhaust path 11 and discharged to a space at the side of the guide table 1 so that the dust 15 does not swirl up right above the travelling bed 2.