Patent ID: 8878424

Claim:
A spark plug comprising: an insulator having an axial bore extending in a direction of an axis, and a center electrode held in one end portion of the axial bore, the center electrode including a core and an outer layer covering the core, the core being formed from a material higher in thermal conductivity than the outer layer, wherein after heat treatment of application of heat at 1,000° C. for five hours in the atmosphere, the outer layer has: a high-hardness region having a hardness of 190 Hv or higher and a thickness of 30 μm to 200 μm and an element supply region whose subregion in the vicinity of a surface of the outer layer contains Cr in an amount of 15 mass % to 40 mass % and Al in an amount of 0 mass % to 38 mass %, or Al in an amount of 5 mass % to 38 mass % and Cr in an amount of 0 mass % to 40 mass % and whose deeper subregion contains Cr in an amount of 7 mass % to 40 mass % and Al in an amount of 0 mass % to 38 mass %, or Al in an amount of 3 mass % to 38 mass % and Cr in an amount of 0 mass % to 40 mass %, and the element supply region has a thickness of 50 μm or more.