Patent ID: 8324791

Claim:
A spark plug for an internal combustion engine, comprising: a rod-shaped center electrode extending from a leading end thereof to a base end thereof in an axial direction; a substantially cylindrical insulator disposed on an outer periphery of the center electrode and extending from a leading end thereof to a base end thereof in the axial direction; a substantially cylindrical metal shell disposed on an outer periphery of the insulator and extending from a leading end thereof to a base end thereof in the axial direction; a ground electrode comprising a basal end portion joined to a leading end surface of the metal shell and a distal end portion bent toward the center electrode; a first noble metal tip joined to the distal end portion of the ground electrode and opposing a leading end portion of the center electrode so as to define a gap, a part of the first noble metal tip being embedded in the ground electrode, and another part of the first noble metal tip protruding in a protruding direction from a distal end surface of the distal end portion of the ground electrode such that a relationship A≧0.25 mm is satisfied where A (mm) is the protruding length of the first noble metal tip from the distal end surface of the distal end portion of the ground electrode; and a bulge portion covering at least a center part of an exposed portion of the first noble metal tip in a width direction at a boundary between the first noble metal tip and the distal end surface of the ground electrode, wherein the bulge has a rounded or convex shape, and protrudes in the protruding direction from the distal end surface of the distal end portion of the ground electrode.