Provided is a plasma processing apparatus including a microwave radiating mechanism configured to radiate microwaves output from a microwave output unit into a processing container. The microwave radiating mechanism includes: an antenna configured to radiate the microwaves; a dielectric member configured to transmit the microwaves radiated from the antenna, and form an electric field for generating surface wave plasma by the microwaves; a sensor provided in the microwave radiating mechanism or adjacent to the microwave radiating mechanism, and configured to monitor electron temperature of the generated plasma; and a controller configured to determine a plasma ignition state based on the electron temperature of the plasma monitored by the sensor.