A
spark plug that prevents a sharp increase in resistance of a
resistor and materializes an excellent load life performance. The
spark plug has a
resistor formed by heat-sealing of a
resistor composition that contains, at least, a conductive material and glass
powder. The glass
powder contains between 35.0 mol % and 69.8 mol % SiO2, between 15.0 mol % and 49.8 mol % B2O3, between 5.0 mol % and 20.0 mol % Li2O, and at least one additive selected from MgO, CaO, SrO, BaO, Na2O, K2O, ZnO, and ZrO2 in a total of between 2.6 mol % and 25.0 mol %. Further, the total content of Li2O and the additive(s) in the glass
powder is between 15.2 mol % and 45.0 mol %, and the ratio of the Li2O content to the total content of the additive(s) is between 1.3 and 5.0.