A plasma processing apparatus, wherein the energy and density of ions impinging onto a base material can be controlled precisely and the process parameters can be controlled easily too. The apparatus comprises means (9, 12) for measuring the waveshape and value of a high-frequency electric power; a means (13) for calculating the energy and density of ions impinging onto the base material on the basis of the measured values; a means (13) for storing process parameters determined according to the state of a plasma; a means (13) for displaying the output of the storage means; a means (13) for setting the values of energy and density of ions; a means (13) for inputting the energy value and density value of ions to the setting means; and a means (14) for controlling the energy and density of the ions in the apparatus at the values set in the setting means.