Patent ID: 8653726

Claim:
A spark plug comprising: a rod-like center electrode extending along an axis; an insulator provided around the center electrode; a metallic shell provided around the insulator; and a ground electrode which is joined to the metallic shell and which forms a gap in cooperation with the center electrode, the ground electrode including a ground electrode base member and a rectangular parallelepiped-shaped noble metal tip, the ground electrode base member extending from the metallic shell toward the center electrode and having a first base member surface which is an end surface on the side toward the center electrode and a second base member surface adjacent to the first base member surface, the noble metal tip being embedded in the ground electrode base member, through resistance welding, such that the noble metal tip projects from the first base member surface and the second base member surface and having a facing surface which faces the center electrode, wherein a cross section of the ground electrode base member orthogonal to a center axis of the ground electrode base member has a cross-sectional area S which satisfies a relation 1.8 mm 2 ≦S≦3.2 mm 2 , and an embedment depth A and a tip thickness B satisfy a relation 0.4≦(A/B)≦0.8, where the embedment depth A is a depth by which the noble metal tip is embedded in the second base member surface, and the tip thickness B is a thickness of the noble metal tip as measured along a direction in which the noble metal tip is embedded in the second base member surface.