A glaze layer 2d of the spark plug has the composition comprising 1 mol % or less of a Pb component in terms of PbO; 25 to 45 mol % of a Si component in terms of SiO2; 20 to 40 mol % of a B component in terms of B2O3; 5 to 25 mol % of a Zn component in terms of ZnO; 0.5 to 15 mol % of Ba and/or Sr components in terms of BaO or SrO; 5 to 10 mol % in total of at least one alkaline metal component of of Na, K and Li in terms of Na2O, K2O, and Li2, respectively, where K is essential; and further, 0.5 to 5 mol % in total of one or two kinds or more of Mo, W, Ni, Co, Fe and Mn in terms of MoO3, WO3, Ni3O4, Co3O4, Fe2O3, and MnO2, respectively.