Patent ID: 8115372

Claim:
A spark plug for an internal combustion engine, comprising: a cylindrical insulating body having an axial hole extending in an axial direction thereof; a center electrode having a front end surface provided in the axial hole; a cylindrical metal shell provided on an outer circumference of the insulating body; and a ground electrode having a base end provided on a front end portion of the metal shell and a noble metal tip comprising a noble metal having a base end that is bonded to a front end side surface of the ground electrode such that a front end surface of the noble metal tip is opposed to the front end surface of the center electrode, wherein the noble metal tip is bonded to the ground electrode such that a molten bond in which part of the noble metal tip and part of the ground electrode are molten together is formed at an interface between the noble metal tip and the ground electrode, and when viewed in cross-section including a center axis of the noble metal tip along a longitudinal direction of the ground electrode, a sum of a cross-sectional area of a base-end-side molten bond (A) positioned at a base end side of the ground electrode and a cross-sectional area of a front-end-side molten bond (B) positioned at a front end side of the ground electrode is equal to or greater than 4 mm 2 , and the cross-sectional area of the front-end-side molten bond (B) is 1.1 to 1.3 times greater than that of the base-end-side molten bond (A).