A plasma processing method for processing a substrate includes a discharge beginning step of supplying a second high-frequency power into a processing chamber through an impedance matching circuit and then supplying a first high-frequency power larger than a power used in processing into the processing chamber to generate a plasma. An adjustment step of reducing the first high-frequency power to be close to the value used in processing, increasing the second high-frequency power to be close to the value in processing, and then adjusting the first high-frequency power to obtain a plasma strength of a predetermined value is part of the method. The plasma processing step of causing the impedance matching circuit to perform a matching operation and simultaneously adjusting the first high-frequency power to obtain a plasma strength of a desired value in processing is also part of the method. Plasma discharge can be automatically, smoothly begun with high reproducibility, and stable plasma discharge can be maintained. Even in the case of disappearance of discharge, plasma discharge can be quickly restarted.