PURPOSE: To improve both airtightness and assemblability by using a solder of a low melting point as a brazing material for fixing the holder, also heating the opening part locally and swiftly by using a coil heater, and melting the solder.

CONSTITUTION: A solder whose melting point is comparatively low is used for a brazing material 19 which fills the space 18 between the opening part 6 of the cap 5, and the holder 8, and brazes both of them, and it is formed in a ring-shape of a solder wire and is placed on the end of the opening part 6. Subsequently, a coil heater 20 is placed so as to surround the opening part 6, the electric power supply is turned on, only the inside of the heater 20 is heated locally, and the solder 19 is melted. As a result, the molten solder flows into the gap 18 between the holder 8 and the opening part 6, and the holder 8 and the opening part 6 are fixed firmly. Accordingly, the lower part of the cap 5 and the stem 2 are not heated at all, and it is possible to prevent such a trouble as the solder for mixing the silicon submount 3 is melted.