In a spark plug, a center electrode includes a base member and a discharge chip that has a higher melting point than the base member. The base member and the discharge chip are joined to each other by both a weld and a diffusion layer. The weld is formed, by fusion welding, along an outer periphery of an interface between the base member and the discharge chip into an annular shape. The weld is made up of those parts of the base member and the discharge chip which are molten and mixed together during the fusion welding and solidified after the fusion welding. The diffusion layer is formed radially inside the annular weld. The diffusion layer is made up of those parts of the base member and the discharge chip which are diffused into each other across the interface between the base member and the discharge chip.