Disclosed herein is a processing system for applying a cleaning processing to a substrate such as a semiconductor wafer which includes a cleaning processing section including a plurality of process units each serving to apply a predetermined treatment to a wafer and a loading/unloading section 2 The cleaning processing section includes four scrub cleaning units consisting of two scrub cleaning units arranged side by side and two additional cleaning units stacked on the two scrub cleaning units arranged side by side, respectively, so as to form upper and lower stages of the scrub cleaning units, a wafer inversion unit for turning the wafer upside down, a wafer transit unit having the wafer disposed thereon temporarily for performing the transfer of the wafer to and from the transfer section, and a main wafer transfer mechanism.