Patent ID: 8247740

Claim:
A spark plug, comprising: a cylindrical metal shell; a cylindrical ceramic insulator retained in the metal shell; a center electrode retained in the ceramic insulator and extending in an axial direction; a ground electrode formed into a bent shape and having a rear end portion fixed to the metal shell and a front end portion facing a front end portion of the center electrode with a gap left between the front end portion of the ground electrode and the front end portion of the center electrode, the ground electrode including a large thickness region formed on a rear end side thereof with a large thickness, a small thickness region formed on a front end side thereof with a smaller thickness than that of the large thickness region, a protruding region formed on the small thickness region and facing the center electrode and a thickness changing region formed between the large thickness region and the small thickness region and located at a different position from a position of a minimum curvature radius region of the bent shape of the ground electrode; and a noble metal tip disposed on the protruding region.