Abstract: The plasma processing apparatus includes main electrodes 5, 31 opposed to each other with a plasma processing space 15 interposed therebetween. The plasma processing apparatus further has a side electrode 6 opposed to side faces 5B-1, 5B-2 of the main electrode 5, as well as a side electrode 32 opposed to side faces 31B-1, 31B-2 of the main electrode 31. Therefore, in addition to the plasma processing space 15 between the main electrode 5 and the main electrode 31, an electric field can be formed in spaces between the side faces of the main electrodes 5, 31 and the side electrodes 6, 32, the spaces serving as predischarge areas 16-1, 16-2. By this electric field, processing gas present in the predischarge areas 16-1, 16-2 can be transformed into plasma. Electrons and excitation species of the plasma generated in these predischarge areas 16-1, 16-2 can be supplied directly to the plasma processing space 15.