To eliminate a polishing process of a lead pin and surely conduct soldering by conducting gold plating or silver plating to a part being taken out to the outside of an envelope of the lead pin.

A wire grid 6 is constituted with a plurality of metal wires arranged in parallel at almost the equal distance as an anode between holding members 6b, 6c arranged in parallel, and a part for forming a lead pin is bent in a gull-wing shape. Before the wire grid 6 is formed by using a jig, ends 10, 11, 12 are gold-plated or silver-plated, and an oxide film is formed in a part where frit glass is attached in assembling. The formation of oxide film in a part to be soldered in a production process is unnecessary, and soldering is conducted without polishing after assembly.