To suppress variation in the resistance value of a built-in resistor even when firing is repeated, by setting the softening temperature of glass powder for use in built-in resistor paste and that of glass powder for use in green sheets in a specified relation.

A green sheet using glass powder and an internal circuit containing conductive powder are simultaneously fired to form a low- temperature fired substrate. Letting the softening temperature of glass powder used in built-in resistor paste obtained by dispersing the conductive power and glass powder in vehicle be Tr°C, and the softening temperature of the glass powder for use in the green sheet be Ti°C, Tr and Ti are controlled so that the relation expressed as Ti≥Tr≥Ti-50 will hold. That is, to suppress variation in the resistance value of a built-in resistor due to repeated firing, the softening temperature Tr of glass for use in built-in resistor paste may be made to approach the softening temperature Ti of glass for use in green sheets. This makes it possible to make the resistance value of a built-in resistor resistant to temperature during repeated firing.