A spark plug comprising: a center electrode extending in an axial direction; an insulator having an axial bore which extends in the axial direction and into which the center electrode is inserted; a metallic shell disposed around the insulator; a main ground electrode whose proximal end portion is joined to a forward end portion of the metallic shell and whose distal end portion forms a gap G1 in the axial direction in cooperation with a forward end portion of the center electrode; and three auxiliary ground electrodes (310, 320, 330) whose proximal end portions are joined to the forward end portion of the metallic shell and whose distal end portions form gaps in cooperation with a side surface of the center electrode, wherein facing surfaces of the distal end portions of the three auxiliary ground electrodes (310, 320, 330) which form the gaps in cooperation with the center electrode are located forward of the forward end of the insulator with respect to the axial direction; a first auxiliary ground electrode of the three auxiliary ground electrodes (310, 320, 330) is joined to the metallic shell at a position opposite a position at which the main ground electrode is joined to the metallic shell, with respect to the center electrode; and second and third auxiliary ground electrodes (320, 330) of the three auxiliary ground electrodes (310, 320, 330) are joined to the metallic shell at positions opposite to each other with respect to the center electrode, the spark plug being characterized in that, when a width of the first auxiliary ground electrode is represented by W, a shortest distance between the second auxiliary ground electrode and the third auxiliary ground electrode is represented by T, and a distance which is a component of the shortest distance T in a direction orthogonal to the first auxiliary ground electrode is represented by Tp, a relation W ≥ Tp is satisfied. a center electrode extending in an axial direction; an insulator having an axial bore which extends in the axial direction and into which the center electrode is inserted; a metallic shell disposed around the insulator; a main ground electrode whose proximal end portion is joined to a forward end portion of the metallic shell and whose distal end portion forms a gap G1 in the axial direction in cooperation with a forward end portion of the center electrode; and three auxiliary ground electrodes (310, 320, 330) whose proximal end portions are joined to the forward end portion of the metallic shell and whose distal end portions form gaps in cooperation with a side surface of the center electrode, wherein facing surfaces of the distal end portions of the three auxiliary ground electrodes (310, 320, 330) which form the gaps in cooperation with the center electrode are located forward of the forward end of the insulator with respect to the axial direction; a first auxiliary ground electrode of the three auxiliary ground electrodes (310, 320, 330) is joined to the metallic shell at a position opposite a position at which the main ground electrode is joined to the metallic shell, with respect to the center electrode; and second and third auxiliary ground electrodes (320, 330) of the three auxiliary ground electrodes (310, 320, 330) are joined to the metallic shell at positions opposite to each other with respect to the center electrode, the spark plug being characterized in that, when a width of the first auxiliary ground electrode is represented by W, a shortest distance between the second auxiliary ground electrode and the third auxiliary ground electrode is represented by T, and a distance which is a component of the shortest distance T in a direction orthogonal to the first auxiliary ground electrode is represented by Tp, a relation W ≥ Tp is satisfied.