The present invention is a plasma processing apparatus that includes a processing chamber where plasma processing is performed on a sample, a radio frequency power supply that supplies radio frequency power to generate plasma, a sample stage on which the sample is placed, and a gas supply unit that supplies a gas to the processing chamber. The gas supply unit includes a first pipe that supplies a first gas as a gas for etching process to the processing chamber, a second pipe that supplies a second gas as a gas for etching process to the processing chamber, and a third pipe through which a third gas as a gas for deposition process flows. The third pipe is coupled to the second pipe. A fourth valve is arranged on the second pipe. The fourth valve prevents the third gas from flowing in a direction toward a supply source of the second gas.