PURPOSE: To improve the insulating property between an external lead wire and a stem wire by connecting the stem wire passed through an insulating cylinder provided along a light emitting tube to one of external lead wires externally delivered from the sealed parts of the light emitting tube, and fixing one end of the cylinder to a base.

CONSTITUTION: A pair of electrodes 2a, 2b are provided in the inner part of a light emitting tube 1 made of quartz, and external lead wires 5, 6 are externally delivered from the sealed parts 3, 4 on both the ends of the tube. A stem wire 7 passed through a tube 9 consisting of an insulating material provided along the light emitting tube 1 is connected to one lead wire 5. One end of the cylinder is fitted to a hole 11 provided on a cylindrical base 10 consisting of a heat resisting resin, and fixed by a heat resisting cement 12.