A spark plug comprising: a rod-like center electrode extending in a direction of an axis; an approximately cylindrical tubular insulator provided on the periphery of the center electrode; an approximately tubular metallic shell provided on the periphery of the insulator; and a main ground electrode and at least two auxiliary ground electrodes having respective proximal end portions joined to a front end portion of the metallic shell, wherein the main ground electrode is disposed so that its distal end portion faces a side surface of a front end portion of the center electrode and forms a main spark discharge gap between the distal end portion and the front end portion of the center electrode; each of the auxiliary ground electrodes is disposed so that a portion of its distal end portion end surface faces an outer circumferential surface of a front end portion of the insulator; characterised in that a total area S satisfies an expression S/Av < 1.3, which represents a relation between the total area S and an average gap distance Av (mm) of the main spark discharge gap, where the total area S is the sum of a projection area C of a portion of the distal end portion of the main ground electrode which overlaps with a projected region of the front end portion of the center electrode, both projections along a radial direction of the center electrode, and a projection area D (mm 2) of a portion of the front end portion of the center electrode which overlaps with a projected region of the distal end portion of the main ground electrode, both projections along a radial direction of the center electrode. a rod-like center electrode extending in a direction of an axis; an approximately cylindrical tubular insulator provided on the periphery of the center electrode; an approximately tubular metallic shell provided on the periphery of the insulator; and a main ground electrode and at least two auxiliary ground electrodes having respective proximal end portions joined to a front end portion of the metallic shell, wherein the main ground electrode is disposed so that its distal end portion faces a side surface of a front end portion of the center electrode and forms a main spark discharge gap between the distal end portion and the front end portion of the center electrode; each of the auxiliary ground electrodes is disposed so that a portion of its distal end portion end surface faces an outer circumferential surface of a front end portion of the insulator; characterised in that a total area S satisfies an expression S/Av < 1.3, which represents a relation between the total area S and an average gap distance Av (mm) of the main spark discharge gap, where the total area S is the sum of a projection area C of a portion of the distal end portion of the main ground electrode which overlaps with a projected region of the front end portion of the center electrode, both projections along a radial direction of the center electrode, and a projection area D (mm 2) of a portion of the front end portion of the center electrode which overlaps with a projected region of the distal end portion of the main ground electrode, both projections along a radial direction of the center electrode.