PURPOSE: To prevent the damage of cylindrical electrode and elliptical conduction bodies and use them in internal combustion engine or the like for a long period by baking the overall surface of their inside after coating it with ceramics.

CONSTITUTION: A cylindrical electrode body 3 with an air outlet port 1 forward and an air inlet port 2 backward is provided. A nearly elliptical conduction body 5 on the external surface of which a number of peak-shaped electrodes 4 are imbedded is retained inside the said electode body 3 by means of the front and rear support axes 6 and 6'. The air outlet port 2 is provided on an insulating plate 7 and the front support axis 6' is also made of an insulating material. The said cylindrical electrode 3 and elliptical conduction body 5 are connected to a high voltage generation transformer 8 with a constant voltage device through the support axis 6. As a result, the inner surface of the cylindrical electrode body 3 and the elliptical conduction body 5 generate a uniform spark, i.e. corona discharge between both electrodes through the peak-shaped electrodes 4 by the impression of the high voltage generation transformer. These, inside surface generating discharge are all baked and coated with ceramics.