Patent ID: 7224109

Claim:
A spark plug comprising: a metal housing having a fixing screw portion provided on an outer surface thereof so as to be installed to an engine via said fixing screw portion; an insulator fixed in said metal housing, with one end portion protruding from one end portion of said metal housing; a center electrode fixed in an axial hole of said insulator, with one end portion protruding from said one end portion of said insulator; and a ground electrode having one end portion fixed to said metal housing, a bent portion provided at an intermediate portion thereof, and the other end portion positioned in a confronting relationship with said one end portion of said center electrode to form a spark discharge gap, wherein said ground electrode contains either Ni or Fe as a main component and at least one additive selected from the group consisting of Cr and Al, a cross-sectional area of said ground electrode is not less than 2 mm 2 and not greater than 3 mm 2 , and an average value of crystal grain diameters in a thickness direction is not less than 100 μm at least at said bent portion.