Patent ID: 8013503

Claim:
A spark plug for an internal combustion engine, said spark plug comprising: a rod-shaped center electrode extending in a direction of an axis line; a substantially cylindrical insulator disposed on an outer periphery of the center electrode; a cylindrical metal shell disposed on an outer periphery of the insulator; a ground electrode having a base end joined to a leading end portion of the metal shell in the direction of the axis line and a distal end portion bent toward the axis line, said 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; a noble metal tip joined to and partially embedded in an inner peripheral surface of the thin portion, the noble metal tip being disposed to form a gap between the same and the leading end portion of the center electrode; and a bulge portion provided on the inner peripheral surface of the thin portion between the stepped portion and the noble metal tip and formed of substantially a same metal component contained in the ground electrode, wherein, when viewed from a side surface of the ground electrode, a following relationship is satisfied: [a protruding height of the noble metal tip from the inner peripheral surface of the thin portion]≧[a protruding height of the bulge portion from the inner peripheral surface of the thin portion].