To prevent a wafer from slipping in a side direction by installing a gas discharge device for discharging the major part of washing gas from a wafer like article at the edge area of the wafer like article in the periphery.

Between a cover 2 and a substrate 3, an annular gas flow passage 5 is formed. This flow passage 5 is fitted on the substrate 3 so that it leads to an annular gap which is an annular nozzle 6 at the upper surface which is the side facing a wafer W and is connected to the substrate 3. Furthermore, it is fitted to the substrate 3 at the upper surface by a lot of spacers of the gas discharge device 4 regularly arranged in the periphery. Between the gas discharge device 4 and the substrate 3, an annular gas discharge flow passage 8 is formed, and gas is discharged from the discharge flow passage 8 by the gas discharge device 4. In this way, in an area 7 outside the annular nozzle 6, a gas cushion is formed, and on the gas cushion, the wafer W is made to float.