To attain reliable starting by stabilizing a starting characteristic even if a cold cathode is displaced.

Electrodes 2a and 2b are sealed in and installed on both ends, and an auxiliary electrode 6 whose one end is connected to a power source is arranged in the tube axis direction on an outside surface of a bulb 1 inside which rare gas is sealed, and a conductive member 7 extending in the circumferential direction is arranged on the other end of this auxiliary electrode 6. Therefore, since the conductive member 7 extending in the circumferential direction of the bulb is arranged on the tip of the auxiliary electrode 6, even if the electrode 2b is displaced from the bulb center, it does not become more distant from the conductive member 7. Therefore, a distance between the electrode 2b and the conductive member 7 can be kept equal to or smaller than a specific value, and dispersion of a starting characteristic can be reduced.