Patent ID: 7839064

Claim:
A spark plug comprising: a center electrode extending in an axial direction of said spark plug; a substantially cylindrical insulator disposed on an outer circumference of said center electrode; a cylindrical metal shell disposed around said insulator; and a ground electrode including a bent portion bent at an intermediate portion of said ground electrode so that a rear end portion of said ground electrode is bonded to a leading end portion of said metal shell and a leading end portion of said ground electrode is opposed to a leading end face of said center electrode, wherein a spark discharge gap is provided between the leading end portion of said center electrode and the leading end portion of said ground electrode, and said ground electrode having a substantially circular or elliptical cross-section, the cross-section having a peripheral surface disposed along a side opposite to a side in which said center electrode is provided, and a maximum width of said ground electrode within a range of ±1 mm from a center point of said spark discharge gap in the axial direction, as viewed in a direction where said center electrode and said ground electrode overlap, is 101-105% of a width of an ordinary portion having a substantially constant width.