PURPOSE: To seal a glass vessel with no residual internal stress, by connecting a vacuum exhaust system to the exhaust port of the vessel, evacuating the vessel, shifting a plug sealed in the exhaust system to the exhaust port of the vessel, and melt-bonding the exhaust port and the plug together by heating.

CONSTITUTION: An exhaust pipe 8 as a part of a vacuum exhaust system is connected to the exhaust port 2 of a glass vessel 1 with a pipe joint 10 (Geissler port), and a glass plug 3 supported on a support rod 5 having a magnetic body 6 at the lower part is sealed in a branch path 4 attached to the pipe 8 at a part just under the port 2. The vessel 1 is evacuated to a prescribed degree of vacuum through the pipe 8, an electromagnetic coil 7 is moved upward, and the plug 3 is shifted and inserted into the prescribed position of the port 2 by the magnetic force of the coil 7 through the magnetic body 6 and the rod 4. The port 2 and the plug 3 are then melt-bonded together by heating with an electric heater 9 to vacuum-seal the vessel 2.