Spark plug

A spark plug comprising:

• a center electrode and a ground electrode having a gap between the center electrode and the ground electrode,
• wherein the ground electrode has at least a core portion and an outer layer covering the core portion,
• the core portion is formed from a material having higher thermal conductivity than that of the outer layer,
• at least a portion in which thickness of the outer layer is 0.5 mm or less exists at a cross-section perpendicular to a direction in which the ground electrode is extended, and
• composition of electrode material forming the outer layer is as follows:
• Ni is 96 mass % or more, total of at least one kind selected from a group consisting of Y and rare earth elements is 0.05 mass % or more, Al is 0.5 mass % or less, and Si is 0.5 mass % or more and 1.5 mass % or less (here, total of Ni, Y, rare earth elements, Al, Si does not exceed 100 mass %).