PURPOSE: To assemble while simplifying a process by attaching a cover able to be tightly fitted through a solder material to an exhaust port provided on one part of a vacuum container for sealing the vacuum container in a state of a high temperature vacuum.

CONSTITUTION: The container 2a holding an electrode 4a and the container 2b holding an electrode 4b are assembled through insulators 3 for forming a vacuum container. Thereby, one part of the container 2a is provided with an exhaust port 8 processed by spot facing while attaching a cover 7 able to be tightly fitted thereto through a solder material 62 and the wax materials 6aW6d are arranged on the junction parts of the containers 2a, 2b with the electrodes 4 as well as with the insulators 3 respectively for sealing while melting each wax material 5 in a vacuum of high temperature in order to hold the vacuum. Accordingly, exhaust, heating and a sealing process are simultaneously performed to simplify assembly while making handling easy by doing away with an outward projection such as an exhaust pipe or the like.