PURPOSE: To prevent floating contaminants from being readhered on silicon wafers by a method wherein cleaning units, which are respectively provided with a transfer device for transferring a wafer carrier and cleaning sprays, are connected to each other via an atmosphere separating device.

CONSTITUTION: Cleaning sprays 1 are used instead of a cleaning tank and wafer carriers 5 housing silicon wafers 4 are respectively transferred in cleaning units 3A to 3D by each transfer device 2 while the wafers 4 are sprayed a cleaning liquid from the sprays 1. The wafers 4 transferred while being sprayed the cleaning liquid pass an atmosphere separating device 6, such as an automatic opening and shutting shutter or the like, and are transferred in the following cleaning units. Thereby, it is eliminated that contaminants peeled from the wafers 4 remain in the cleaning tank and are readhered on the wafers.