The invention provides a plasma processing method which includes (i) feeding a transferring gas which decreases a pressure difference between a processing chamber and a transfer chamber in order to prevent particles from adhering a processing sample, to be processed, passed to the processing chamber, before transferring the sample into the processing chamber; (ii) transferring the sample into the processing chamber while continuing to feed the transferring gas to the processing chamber; (iii) generating a plasma from the transferring gas in the processing chamber while continuing to feed the transferring gas to the processing chamber after the step of transferring the sample; and (iv) changing a gas supplied to the processing chamber from the transferring gas used in the step of generating the plasma to a processing gas for subjecting the processing sample, different from a cleaning sample, to plasma processing.