PURPOSE: To improve a welding performance and welding operability by performing a TIG welding of a welding place with closely fitting the cylindrical body of the other part supported by a flexible rotary type conductive coupler to the rotary cylindrical body of one part.

CONSTITUTION: An envelop main body 1 is placed on a guide reel 10 and driving reel 12 and the electrode armature 21 of a coupler 13 is brought into contact with the input window 2 of the body to be welded as well. A welding place A is subjected to a TIG welding by a welding torch 6 with rotating the main body 1 and input window 2 by driving the reel 12 by a motor 11. With the device of this composition an airtight product of excellent quality can be manufactured with good efficiency.