An object of the invention is to restrain separation of an electrode tip from a ground electrode or from a center electrode. A spark plug satisfies a condition 0.8≦A1/A2≦1.9, where, as viewed on a section which contains a center axis (O) of an electrode tip, A1 [Hv] is hardness of the electrode tip as measured outside a circle having a radius of 0.2 mm, with a boundary point (PA) on a surface of the spark plug between a fusion zone and the electrode tip serving as the center of the circle, and A2 [Hv] is hardness of the electrode tip as measured within the circle having a radius of 0.2 mm.