A spark plug for an internal combustion engine includes a housing, an insulator, and a center electrode. The center electrode includes an inside electrode portion and an outside electrode portion. The housing includes a ground electrode projecting from a distal end portion of the housing toward the distal end side of the plug at a part in a plug circumferential direction. The outside electrode portion projects along a surface of the insulator tip in a direction away from a boundary with the inside electrode portion and includes a projection, which is capable of causing an electrical discharge between the ground electrode and the outside electrode portion. The projection is formed in a region in the plug circumferential direction. The projection and the ground electrode are located at positions different from each other in the plug circumferential direction.