Patent ID: 8319409

Claim:
A spark plug for an internal combustion engine, comprising: a rod-shaped center electrode that extends in an axial direction of the spark plug; a tubular insulator having an axial hole that extends in said axial direction of the spark plug in which said center electrode is received; a tubular metal shell disposed along an outer circumference of said insulator; and a ground electrode which extends from a tip end portion of said metal shell and is disposed in such a bent state that a tip end portion thereof is opposed to said center electrode; wherein a tip end portion of said center electrode and the tip end portion of said ground electrode cooperate to define a gap therebetween in which spark discharge is provided along said axial direction of the spark plug, wherein said ground electrode is formed with a narrowed width portion at the tip end portion thereof which has a substantially uniform width smaller than an outer diameter of a tip end surface of said center electrode, and a widened width portion which extends between a base end portion of said ground electrode and said narrowed width portion and has a width larger than the width of said narrowed width portion, wherein said narrowed width portion has a base end that is located offset from the tip end surface of said center electrode toward a root side of said ground electrode when viewed from a tip end side of the spark plug in said axial direction of the spark plug, and wherein said base end of the narrowed width portion is located offset from a center of said gap toward the tip end side of the spark plug in said axial direction of the spark plug.