Provided is a feature of a multilayered ground electrode wherein an outer layer and an inner layer can be kept peeling away from each other. A spark plug is provided with: a cylindrical main fitting; an insulator having a shaft hole along the axis, at least a part of the outer periphery of the insulator being held by the main fitting; a center electrode provided to the shaft hole; and a ground electrode affixed to the main fitting. The ground electrode has an outer layer and an inner layer covered by the outer layer, the inner layer having higher heat conductivity than the outer layer. Taking L1 to be the width of the inner layer along the width direction of the ground electrode and L2 to be the width-direction dimension of an oxide present between the outer layer and the inner layer, the ratio L of L2 to L1 (L2/L1) is 5-50%.
