PURPOSE: To acquire the good electrical continuity condition even when a low voltage is being applied by providing the connecting part of Al lead wire and Ag lead wire within a vacuum external case and covering it with a carbon film.

CONSTITUTION: A lead wire 1 consisting of Al thin film is provided on a glass substrate 2, the lead wire 1 is not formed up to the terminal part and it is remained at the inside of vacuum external case surrounded by the face glass 3. Next, the Ag lead wire 4 is stacked on the Al lead wire 1 by the thick film printing method so that the lead wire 4 forms a part of internal lead wire from the terminal part of vacuum external case. A carbon film 5 formed by the thick film printing method is provided in order to cover the connecting part using graphite or carbon powder having excellent conductivity. Moreover, an over-coat glass 6 is formed in such a way as covering the entire part of the substrate 2 where these lead wires and carbon film 5 are provided.