PURPOSE: To prevent an airtight-sealing defect from being caused by a method wherein regions whose softening temperature is different are formed in sealing materials on a ceramic substrate, the sealing material having a low softening temperature is melted and, when an internal air pressure has become the same as a pressure on the outside, the sealing material having a high softening temperature is melted.

CONSTITUTION: A sealing part 15 made of a ceramic is fixed and bonded to the outside on the surface of a ceramic substrate 11; the surface is coated with a first PbO-based low-melting-point glass having a softening temperature of 400 to 420°C; and the peripheral part of a ceramic lid plate 17 is coated with a sealing material. Central parts of individual sides are coated with a second PbO-based low-melting-point glass in which slits 19 have been formed. Its softening temperature is at 450 to 470°C and is higher than that of the first low-melting-point glass. This assembly is heated to about 430°C; it is then heated to about 480°C; and it is sealed. When the assembly is heated at about 430°C, a gas escapes through the slits 19. Even when its temperature is raised to about 480°C, an internal pressure is raised only slightly and an airtight-sealing defect is prevented.