PURPOSE: To facilitate encapsulation of amalgam by applying amalgam or metallic body onto the surface of a thin tube then inserting the thin tube into an exhaust tube and encapsulating inert gas and mercury through the thin tube into a light emission bulb thereafter sealing the thin tube and exhaust tube through welding.

CONSTITUTION: Phosphor substance 2 is coated onto the inner face of a light emission bulb 1 while the flare section 5 of a stem 4 constructing a mount 3 is sealed at the opening at the opposite ends of bulb 1. Lead wires 7, 7 are sealed air-tightly to the stem tube 6 of stem while an exhaust tube 10 opening to the inner space 9 of bulb 1 is projected. A thin glass tube 11 is inserted into the exhaust tube 10 through a gap 12 against the innercircumferential face of the exhaust tube 10 while metal body 13 which will bond with mercury to form amalgam is applied onto the outer face at the end of insertion of the thin tube 11. Then predetermined amount of mercury 16 and inert gas are encapsulated in the bulb 1 through the thin tube 11 and the exhaust tube 10 is heated by a burner 14 to seal the thin tube 11 and the exhaust tube 10 integrally through welding.