| 摘要 |
A tip portion of a center electrode 2 of a spark plug includes a tapered portion which is tapered such that the diameter reduces axially frontward. A convex portion 2k is formed at an axially intermediate position of the tapered portion so as to project radially outward with respect to an axis 30. The axially measured distance L2 between the vertex of the convex portion 2k (the convex vertex P) and the tip face 1D of an insulator is set to less than 0.5 mm. A heat release acceleration metal portion 2m, which is made of Cu or an alloy that contains a predominant amount of Cu, is present at a position located a distance L3 of 1.5 mm as measured axially rearward from the convex vertex P in order to suppress spark erosion by lowering the temperature of the center electrode 2. The heat release acceleration metal portion 2m is formed such that an electrode base material 2n, which encloses the heat release acceleration metal portion 2m, has a wall thickness W of not less than 0.6 mm as measured at a position located 1.5 mm axially rearward from the convex vertex P.
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