Disclosed is a plasma processing apparatus including a processing container, a plasma generation mechanism, a regulation unit, a detection unit, and a determination unit. The plasma generation mechanism includes a microwave oscillator, and generates plasma within the processing container using microwaves oscillated by the microwave oscillator. The regulation unit regulates an oscillation frequency, which corresponds to a frequency of the microwaves oscillated by the microwave oscillator, to a predetermined frequency. The detection unit detects the oscillation frequency regulated to the predetermined frequency by the regulation unit. The determination unit determines the success/failure of regulation of the oscillation frequency by the regulation unit, using the oscillation frequency detected by the detection unit, or using a parameter which is changed depending on a difference between the oscillation frequency and the predetermined frequency.