A spark plug comprising: a tubular metal shell; an insulator having at least a part of an outer circumference thereof held by the metal shell and having an axial hole; a center electrode provided in the axial hole; a ground electrode having a base end portion fixed to the metal shell, and having one side surface, of a front end portion of the ground electrode, opposing an end surface of the center electrode through a gap; and a noble metal tip provided on the one side surface side of the ground electrode, said noble metal tip having a front end that projects forward of the front end portion of the ground electrode, wherein an end surface of the front end portion of the ground electrode and the front end of the noble metal tip are positioned between an imaginary straight line and a centerline of the center electrode, said imaginary straight line being parallel to the centerline of the center electrode and passing through an end point, of the end surface of the center electrode, said end point being disposed on a side opposite to a side closer to the base end portion of the ground electrode, characterized in that when S1 represents an area of an overlap region in which a region onto which the end surface of the center electrode is projected overlaps a region onto which the noble metal tip is projected when the noble metal tip and the end surface of the center electrode are projected onto an imaginary plane perpendicular to the centerline, and S2 represents an area of an overlap region in which a region onto which the noble metal tip is projected overlaps a region onto which the ground electrode is projected when the noble metal tip and the ground electrode are projected onto the imaginary plane, 0.22≤S1/S2≤0.68 is satisfied. a tubular metal shell; an insulator having at least a part of an outer circumference thereof held by the metal shell and having an axial hole; a center electrode provided in the axial hole; a ground electrode having a base end portion fixed to the metal shell, and having one side surface, of a front end portion of the ground electrode, opposing an end surface of the center electrode through a gap; and a noble metal tip provided on the one side surface side of the ground electrode, said noble metal tip having a front end that projects forward of the front end portion of the ground electrode, wherein an end surface of the front end portion of the ground electrode and the front end of the noble metal tip are positioned between an imaginary straight line and a centerline of the center electrode, said imaginary straight line being parallel to the centerline of the center electrode and passing through an end point, of the end surface of the center electrode, said end point being disposed on a side opposite to a side closer to the base end portion of the ground electrode, characterized in that when S1 represents an area of an overlap region in which a region onto which the end surface of the center electrode is projected overlaps a region onto which the noble metal tip is projected when the noble metal tip and the end surface of the center electrode are projected onto an imaginary plane perpendicular to the centerline, and S2 represents an area of an overlap region in which a region onto which the noble metal tip is projected overlaps a region onto which the ground electrode is projected when the noble metal tip and the ground electrode are projected onto the imaginary plane, 0.22≤S1/S2≤0.68 is satisfied.