Patent ID: 8013504

Claim:
A spark plug for an internal combustion engine, said spark plug comprising: a rod-shaped center electrode extending in the direction of an axis line; a substantially cylindrical insulator provided on an outer periphery of the center electrode; a cylindrical metal shell provided on an outer periphery of the insulator; a ground electrode having a base end joined to a leading end portion of the metal shell and a distal end bent toward the axis line, the ground electrode comprising: a thick portion provided on a base end side, a thin portion provided on a distal end side, and a stepped portion provided on an inner peripheral surface between the thick portion and the thin portion; and a first noble metal tip joined to and partially embedded in the inner peripheral surface of the thin portion, the first noble metal tip being disposed to form a gap between the first noble metal tip and the leading end portion of the center electrode, wherein a relationship B/A≦2.5 is satisfied where, when viewed from a side surface of the ground electrode, A (mm) is a thickness of the thick portion of the ground electrode, and B (mm) is a distance between the base end of the inner peripheral surface of the ground electrode and a distal end surface of the ground electrode in the horizontal direction.