A spark plug comprising: an insulator having an axial hole; a metal shell surrounding an outer circumference of the insulator; a center electrode having a center electrode base material disposed in the axial hole and an electrode tip joined to the center electrode base material and exposed outside from a front end portion of the metal shell; and a ground electrode having a fixed end portion fixed to the metal shell and a free end portion located at a predetermined gap apart from a front end of the electrode tip, the ground electrode having: an inner surface facing the center electrode and the insulator; and an outer surface (30d, 30e) connecting one end to the other end of the inner surface in a width direction of the ground electrode and including a back surface located opposite the inner surface, the ground electrode having a center electrode-facing site opposed to and facing the center electrode, and a coating part formed of noble metal or noble metal alloy on the ground electrode, characterized in that the coating part is formed on only a region of the outer surface continuing to the inner surface and at least a region of the inner surface from a first intersection to a second intersection, where the first intersection is defined as containing an intersection point at which an imaginary line extending from an outer circumference of the center electrode base material at a side of the fixed end portion to the ground electrode intersects the ground electrode; and the second intersection is defined as an intersection at which an imaginary plane passing through a midpoint of the predetermined gap and extending in parallel with an end face of the front end intersects the ground electrode; the spark plug satisfies a relationship of 0.7F ≤ A ≤ B where A is a dimension of the coating part in the width direction; B is a dimension of the ground electrode in the width direction; and F is a width of the front end of the electrode tip; when the center of the coating part and the center of the front end of the electrode tip are projected onto a plane parallel with the width direction of the ground electrode, a horizontal distance between those two projected center points is half or less of the dimension of the coating part in the width direction. an insulator having an axial hole; a metal shell surrounding an outer circumference of the insulator; a center electrode having a center electrode base material disposed in the axial hole and an electrode tip joined to the center electrode base material and exposed outside from a front end portion of the metal shell; and a ground electrode having a fixed end portion fixed to the metal shell and a free end portion located at a predetermined gap apart from a front end of the electrode tip, the ground electrode having: an inner surface facing the center electrode and the insulator; and an outer surface (30d, 30e) connecting one end to the other end of the inner surface in a width direction of the ground electrode and including a back surface located opposite the inner surface, the ground electrode having a center electrode-facing site opposed to and facing the center electrode, and a coating part formed of noble metal or noble metal alloy on the ground electrode, characterized in that the coating part is formed on only a region of the outer surface continuing to the inner surface and at least a region of the inner surface from a first intersection to a second intersection, where the first intersection is defined as containing an intersection point at which an imaginary line extending from an outer circumference of the center electrode base material at a side of the fixed end portion to the ground electrode intersects the ground electrode; and the second intersection is defined as an intersection at which an imaginary plane passing through a midpoint of the predetermined gap and extending in parallel with an end face of the front end intersects the ground electrode; the spark plug satisfies a relationship of 0.7F ≤ A ≤ B where A is a dimension of the coating part in the width direction; B is a dimension of the ground electrode in the width direction; and F is a width of the front end of the electrode tip; when the center of the coating part and the center of the front end of the electrode tip are projected onto a plane parallel with the width direction of the ground electrode, a horizontal distance between those two projected center points is half or less of the dimension of the coating part in the width direction.