A spark plug includes a center electrode, an insulator holding the center electrode inserted thereinto, a housing holding the insulator inserted thereinto and a ground electrode joined to the housing so as to form a spark discharge gap with the center electrode. The center electrode includes a core member and a cover layer covering a surface of the core member. The core member includes a large-diameter portion made of a material having a thermal conductivity higher than that of the cover layer, a small-diameter portion extending from the large-diameter portion toward a distal end side of the core member, and a connecting portion connecting the large-diameter portion to the small-diameter portion. The cover layer is made of a material having a linear expansion coefficient lower than that of the core member, and covers between at least part of the connecting portion and a distal end of the small-diameter portion.