The present invention provides a plasma processing apparatus which reduces damage from plasma generated in a discharge vessel and lengthens the replacement cycle of the discharge vessel. A plasma processing apparatus 1 is provided with a processing chamber 2 partitioning a processing space, a discharge vessel 3 whose one end opens facing inside the processing chamber 2 and the other end is closed, an antenna 4 which is disposed around the discharge vessel 3 and generates an induced electric field to generate plasma in the discharge vessel 3 under reduced pressure, and an electromagnet 9 which is arranged around the discharge vessel 3 and forms a divergent magnetic field in the discharge vessel 3. The discharge vessel 3 has at its closed end portion a protrusion 15 projecting toward the processing chamber 2.