In a processing system adapted for processing an object to be processed, by supplying a processing fluid into a processing vessel, the supply of the processing fluid into the processing vessel is significantly stabilized. This processing system includes the processing vessel configured to contain the object to be processed, a processing fluid generating unit configured to generate the processing fluid, a processing-side fluid passage configured for supplying the processing fluid generated in the processing fluid generating unit into the processing vessel, and a discharge fluid passage configured for discharging the processing fluid from the processing vessel. The processing system further includes a bypass-side fluid passage connected with the discharge fluid passage at its downstream end and configured for discharging the processing fluid generated in the processing fluid generating unit without passing it through the processing vessel, a pressure control mechanism provided to the discharge fluid passage downstream from a position in which the downstream end of the bypass-side fluid passage is connected with the discharge fluid passage, and a switch valve configured to selectively switch a fluid passage, through which the processing fluid generated in the processing fluid generating unit is fed, between the processing-side fluid passage and the bypass-side fluid passage.