To provide a plasma processing apparatus which allows the execution of an efficient plasma processing, makes it easier to isolate electrodes, and enables the suppression of surface discharge along an inner wall.

A plasma processing apparatus 1000 includes a chamber 1010 made of an insulator and having a flow path 1018. The chamber has a groove 1036 formed in an inner wall 1034 surrounding the flow path 1018 and extending in a direction in non-parallel with an axial direction of the flow path 1018. In the chamber, second and third electrodes 1014 and 1016 are located upstream and downstream of the flow path 1018 from a first electrode 1012 respectively. The first and second electrodes 1012 and 1014 are opposed to and spaced apart from each other in the axial direction of the flow path 1018. The first and third electrodes 1012 and 1016 are opposed to and spaced apart from each other in the axial direction of the flow path 1018. The first electrode 1012 is electrically connected with a first pole of a pulse power source 1004. The second and third electrodes 1014 and 1016 are electrically connected with a second pole of the pulse power source 1004.