PURPOSE: To manufacture an inexpensive airtight glass-sealed window by using a metallic outside ring having a step part in its inner wall, a holeless transparent glass plate, an internal mold jig with through hole, and an upper mold jig with projection.

CONSTITUTION: An airtight glass-sealed window is obtained without the needs to bore a through hole in a transparent glass disk. For example, the metallic outside ring 15 having the tiered portion 16 provided in position on its inner wall is placed on the flat under mold tool 10 of graphite, the transparent holeless glass disk 23 is placed inside the ring 15, and then the ring 15 is covered with the medium mold tool 11 of graphite, having the through hole 12 in its center. Then, the upper mold tool 13 of graphite, having a projection 14 at its center, is pushed down into the tool 11 in such a way as to insert the projection 14 into the through hole 14 in a freely movably manner. The distance (h) between the upside of the medium tool 11 and the downside of the upper tool 13 is made slightly smaller than the depth of a desired concavity. The assembly is wholly put in a furnace of a neutral or weakly reductive atmosphere and then heated at approx. 1,000°C, whereupon the molten glass 26 penetrates into the space 17, and the upper side 26a of the glass is flattened to obtain a desired airtight glass-sealed window.