A plasma processing apparatus includes: a high voltage power supply for supplying a high voltage power to a magnetron; and a detector for detecting a microwave output from the magnetron, wherein based on a result of comparing a signal, which is obtained by adding an output from the detector to an AC component of a current detected from an output of the high voltage power supply, with a setting value of the output of the high voltage power supply, the output of the high voltage power supply is adjusted.