PURPOSE: To seal an opening of a cylindrical glass tube with a sheet-shaped ion responsive glass joined on an end face of the opening thereof, by making the ion responsive glass abut the end face of the opening of the glass tube to apply a DC voltage between both the components under heating.

CONSTITUTION: A sheet-shaped pH responsive glass 2 is made to tightly abut an end face 3A of a glass tube 3 and a DC voltage is applied for 3W5min, for instance, between both the components 2 and 3 under heating. Ions are generated on the interface between both the components 2 and 3 tightly abutting each other; with the mutual electrostatic attraction of ions, the pH responsive glass 2 joins integral with the end face 3A of the opening of the glass tube 3 and one opening of the glass tube 3 is sealed up to form a specified pH responsive glass film M. Direct glass-oriented joining between the pH responsive glass 2 and the glass tube 3 achieves a higher airtightness and electric insulation at a joint 8.