A processing method which, when an organic film layer such as a PR film layer 202 formed on the surface of a wafer W is to be removed from an SiO.sub.2 film layer 204 below it by generating plasma of a process gas in a chamber 1 comprises the step of using O.sub.2 gas as the process gas to remove the organic film layer at a first pressure, e.g., 20 mTorr, lower than in a conventional case, and the step of using the same O.sub.2 gas to remove the organic film layer at a second pressure, e.g., 200 mTorr, higher than the first pressure.