In a plasma processing apparatus, in a matching circuit intervening between a high-frequency power source and a plasma excitation electrode for achieving impedance matching between the high-frequency power source and the plasma excitation electrode, one of the two electrodes which form a tuning capacitor also serves as the plasma excitation electrode. Alternatively, in a plasma processing apparatus, the side wall of a housing made from an electrically conductive member and accommodating a matching circuit intervening between a high-frequency power source and a plasma excitation electrode for achieving impedance matching between the high-frequency power source and the plasma excitation electrode and a feeder for supplying high-frequency electric power from the high-frequency power source to the plasma excitation electrode through the matching circuit is formed not in parallel to the feeder.