| 摘要 |
Separation of a noble metal tip is prevented and wear resistance is enhanced, while the increase in manufacturing cost is suppressed. A spark plug 1 includes a center electrode 5 and a noble metal tip 31. The center electrode 5 and the noble metal tip 31 are joined to each other through a molten portion 35. An area of an interface between the noble metal tip 31 and the center electrode 5 is set to be 5% or less with respect to a cross-sectional area of the noble metal tip 31 which is perpendicular to an axial line CL1 at a portion of an outer surface of the noble metal tip 31 which is nearest to the molten portion 35. In the cross section including the axial line CL1, supposing that a length of the portion of the molten portion 35 in the axial line CL1 which is exposed to the outer surface is A (mm), and a width of the noble metal tip 31 is B (mm), B/A≦̸6 is satisfied. The portion of the molten portion 35, of which a length along the axial line CL1 is A/1.5, is located further outwards radially than a position which comes in by as much as B/4 from the outer circumference of the noble metal tip 31.
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