A plasma processing apparatus that enables polymer to be removed from an electrically insulated electrode. A susceptor of the plasma processing apparatus is disposed in a substrate processing chamber having a processing space therein. A radio frequency power source is connected to the susceptor. An upper electrode plate is electrically insulated from a wall of the substrate processing chamber and from the susceptor. A DC power source is connected to the upper electrode plate. A controller of the plasma processing apparatus determines a value of a negative DC voltage to be applied to the upper electrode plate in accordance with processing conditions for RIE processing to be carried out.