PURPOSE: To obtain a stable main discharge surface by disposing a first electrode pair on the cathode side and a second electrode pair on the anode side with the center section of a discharge space in the center, where the gap of a plurality of pin electrode pairs is spaced almost equally from the discharge surface of the cathode and anode.

CONSTITUTION: First pin electrodes 17a, 17b, the gap 14a of which is positioned in the intermediate section between an axial line 15 passing the center section of a discharge space 9 and the discharge surface of a cathode 1, and second pin electrodes 19a, 19b, the gap 14b of which is positioned in the intermediate section between the axial line 15 and the discharge surface 1 of an anode 2, that is, symmetrically to the gap 14a about the axis line 15 are alternately disposed in the resonance axis direction. Therefore, ultraviolet rays are irradiated into the discharge space uniformly. Even if the discharge surface is irregular due to a sharp angle incidence to discharge surfaces 16, 18, ultraviolet rays are made to strike the inside of a recessed section, and electrons are discharged more uniformly from the entire discharge surfaces 16, 18. As a result, the main discharge surface is stabilized.