PURPOSE: To prevent evaporation of a metallic material from a getter ring and deposition of metal to an insulative thread by coating the getter ring on the funnel side thereof with a deposition film having a steam pressure lower than that of the metallic material constituting the getter ring.

CONSTITUTION: A getter ring 14 is coated on the funnel side and side surface thereof with a deposition film 20 for cutting off a metallic evaporation material constituting the getter ring 14. Namely, a getter container is coated on the funnel side or at the surface on the funnel side and at the side surface with the deposition film 20 made of a material having a steam pressure lower than metal constituting the getter container. Therefore, the metallic evaporation material from the getter ring 14 can be cut off by the deposition film 20 made of the material having the lower steam pressure at the time of getter flash so that deposition of an insulator to an outer peripheral surface can be reduced, thereby preventing any deterioration of an insulative property.