Abstract: An igniter plug comprising: a metallic shell having a diameter-reduced seat at one open end, the seat being tapered to progressively decrease its diameter as approaching at outside of the open end; a tubular insulator concentrically placed at an inner side of the metallic shell, and having a tapered end face to be in registration with the seat; a frusto-cone shaped insert ring made of oxidation and heat resistant material, a peripheral end and one entire surface of which are mounted on a surface of the seat by means of an electrical resistant welding, the insert ring permitting the tapered end face of the insulator to engage with an upper surface of the insert ring; a center electrode concentrically disposed in the insulator, one end of the electrode being terminated short of the tapered end face to allow a creeping discharge to occur along an inner surface of the insulator when a high voltage is applied across the electrode and the insert ring.