A plasma processing apparatus including a processing chamber, a radio frequency power source, a monitoring unit, and a calculation unit is provided. In the processing chamber, etching target film is etched by using plasma. The radio frequency power source supplies radio frequency electric power. The monitoring unit monitors light emission of the plasma. The calculation unit estimates an etching amount of plasma etching of the etching target film based on an emission intensity and a correlation between the etching amount of the etching target film and the emission intensity, the emission intensity being obtained when removing, by using the plasma, a deposition film deposited as a result of the plasma etching.