To provide a long-life, high-performance spark plug for an internal combustion engine.

A center electrode 2 and a grounding electrode 3 are both made using a nickel alloy as a base material and is jointed noble-metal chips 12, 13 to the discharge parts of their respective ends. The noble-metal chip 12 of the center electrode is made of iridium or an iridium alloy and inserted into a hole 20 axially bored in the end of the center electrode. When the outside diameter of the noble-metal chip 12 is A, the outside diameter of the end 21 of the center electrode 2 is B, and the amount by which the noble-metal chip 12 is projected from the center electrode is C, B-A≥0.8×C is preferable within the range of 0.6≤A≤1.2mm and 0.4mm≤C≤1.0mm. When the axial length of the noble-metal chip 12 is E and the distance from the end of the noble-metal chip to the end of an insulator is D, a relation of E≥D should preferably be met.