PURPOSE: To reduce the number of processes and the cost of manufacture by a procedure in which an indium oxide-based conductor is coated on the surface of a transparent tube, electrode is sealed in by heating, and at the same time the conductor layer is insulated from the electrode.

CONSTITUTION: An indium oxide-based conductor is coated on the surface of the glass tube 1 to form the transparent conductor layer 9, and then the glass tube 1 is cut to a desired length. And, one end of the glass tube 1 is sealed with the anode 2 by heating by means of a gas burner, whereby part of the transparent conductor layer 9 at one end of the glass tube 1 is insulated and also made semitransparent. Then, the cathode 5 is housed in the glass tube 1, and the tube is evacuated and filled with xenon gas, etc., and the end portion of the tube 1 is sealed up by heating. Then, after positioning the cathode 5, the glass tube 1 is sealed up by heating and part of the transparent conductor layer 9 is insulated. Afterwards, the unnecessary portions of the glass tube 1 are removed and finishing works, e.g., the fitting of the trigger lead wire 10, etc., are performed.