A spark plug is provided capable of speedily burn off carbon adhered on an insulator. With this spark plug, in order to improve the temperature rise performance of a front end side of an insulator 10, an amount of protrusion H (mm) of the insulator 10, a front-end side volume Vi (mm3) of the insulator 10, and a front-end side volume Vc (mm3) of a center electrode 20 are respectively defined. In consequence, it is possible to improve the recovery property of carbon fouling while retaining the voltage resistance of the insulator 10 and the durability of the center electrode 20. In addition, since the recovery property of carbon fouling improves, it is possible to prevent the occurrence of side sparks generated from the center electrode 20 to a metal shell 50 along the insulator 10, thereby making it possible to stably ensure proper ignition of an air-fuel mixture.