Patent ID: 7352121

Claim:
A spark plug comprising: an insulator having an axial hole formed in an axial direction along an axis of said spark plug; a center electrode disposed in said axial hole of said insulator and on a leading end side of said axial hole; a metal shell surrounding said insulator; and a ground electrode including a ground electrode body having one end joined to said metal shell, and a first precious metal tip formed in other end portion of said ground electrode body so that a leading end surface of said first precious metal tip is disposed opposite said center electrode, wherein: an axial-direction distance t between said leading end surface of said first precious metal tip and an inner circumferential surface of said ground electrode body is not smaller than 0.3 mm; and said spark plug satisfies a relation θ 1 +θ 2 ≦93° in which θ 1 is an included angle between virtual lines s 1 and s 2 , and θ 2 is an included angle between virtual lines s 3 and s 4 , wherein said virtual line s 1 is taken as a line parallel to said axial direction and including the other end side edge on the leading end surface of the first precious metal tip in a section passing through a center of other end surface of said ground electrode body and including said axis, said virtual line s 2 is taken as a line connecting the other end side edge on the leading end surface of said first precious metal tip and a point of intersection between the inner circumferential surface of ground electrode body the and other end surface of the ground electrode body, said virtual line s 3 is taken as a line parallel to said axial direction and including the other end side edge on the leading end surface of said center electrode in the section, and said virtual line s 4 is taken as a line including the other end side edge on the leading end surface of the center electrode and tangent to the insulator.