PURPOSE: To easily provide a sealing part having good airtightness by selecting to a specified value inner diameter of ring-shaped sealant against outer diameter of metal tube.

CONSTITUTION: A sealant 16 which is in contact with a metal tube 5 is formed in a ring shape so that when diameter of a hole 16a installed in the center of the sealant 16 is Dmm and outer diameter of metal tube 5 is dmm, the relations of 0.8≥d and D-d≥3mm are satisfied. The ring-shaped sealant 16 is fixed to the metal tube 5, and melted by heating, and the metal tube 5 and a ceramic closing body 2 are bonded. Since D is larger than d, break of the sealant 16 which may becaused by the metal tube 5 when the sealant 16 is shrunk by heating is prevented. Since relation of D and d is specified, lack of filling amount of sealant in a space between the metal tube 5 and a through hole 2a of the closing body is prevented.