Patent ID: 7764018

Claim:
A gas discharge tube which emits light to an outside from a light exit window of a sealed container in which a gas is sealed by generating discharge between an anode and a cathode which are disposed in the sealed container, comprising: a cylindrical part restricting a discharge path, the cylindrical part being disposed between the anode and the cathode and having a through hole for narrowing the discharge path between the anode and the cathode, the cylindrical part being conductive and being electrically connected to an external power source; and a planar discharge shielding part which is disposed so as to cover a surrounding of the part restricting the discharge path and is electrically insulated from the part restricting the discharge path; wherein the part restricting the discharge path has an end on the cathode side projecting by a predetermined projecting amount more than a surface on the cathode side of the discharge shielding part and an end on the anode side projecting below the entire discharge shielding part into a space where the anode is positioned, and the projecting amount of the part restricting the discharge path to the cathode side is not more than 0.5 mm.