PURPOSE: To make the handling easy, by using such an electron emission material that includes 50 molar percent of barium oxide, 25 molar percent of calcium oxide, and, as an inhibiting agent of isolated barium formation, 5 to 25 molar percent of at least one of niobium oxide, tantalum oxide, hafnium oxide, and so forth.

CONSTITUTION: As the electrode, the one for most common 400-watt high-pressure mercury lamp or 360-watt high-pressure sodium lamp, the core rod of the same being provided with a double coil 1 in contact therewith and single coil 2 on the outside, is used. As the electron emission material 3, a mixture of 50 molar percent of barium oxide carbonate, 25 molar percent of calcium oxide carbonate, and 5 to 25 molar percent of at least one material chosen from the group of niobium oxide, tantalum oxide, hafnium oxide, yttorium oxide, aluminum oxide, and zirconium oxide, is prepared. The electrode is then applied with the above electron emission material being suspended in amyl aluminum acetate and nitrocellulose, and after being dried the same is burned in a weak reducing atmosphere at about 1,800°C to allow the electron emission material to stick thereto.