A plasma processing apparatus includes a stage having a placing surface on which a workpiece is accommodated; a heater provided in the stage and configured to adjust a temperature of the placing surface of the stage; and a controller. The controller is configured to control a supply power to the heater; measure the supply power in a transient state where the supply power to the heater increases and in a second steady state where the supply power to the heater is stable in an extinguished state of plasma; calculate a heat input amount and a heat resistance by performing a fitting on a calculation model that calculates the supply power in the transient state using the heat input amount from the plasma and the heat resistance between the workpiece and the heater as parameters; and calculate a temperature of the workpiece in the first steady state.