A spark plug comprising: a center electrode; a ground electrode; and a noble metal tip that has a spark surface facing the center electrode with a spark gap therebetween and that is joined to a part of the ground electrode near one end of the ground electrode via a fused portion, wherein, when the ground electrode, the noble metal tip, and the fused portion are projected in a direction perpendicular to the spark surface, the fused portion extends outward beyond an outer shape of the noble metal tip so that a part of the fused portion is present at each of positions that are located inward from both side edges of the ground electrode and separated from the side edges in a width direction of the ground electrode, and the fused portion includes a fused protrusion that is located near at least one of two side edges of the noble metal tip in the width direction of the ground electrode and that protrudes in a direction away from the one end; wherein, when the ground electrode, the noble metal tip, and the fused portion are projected in the direction perpendicular to the spark surface, and when a maximum tip width of the noble metal tip in the width direction of the ground electrode is denoted by W, a straight line that passes through a center of the noble metal tip and that extends in a longitudinal direction perpendicular to the width direction is denoted by La, a contact line that is in contact with the one of the side edges of the noble metal tip and that extends in the longitudinal direction is denoted by Lb, a first position, which is a position on the fused portion that is within a distance of ±W/4 from the straight line La in the width direction and that is farthest from the one end of the ground electrode, is denoted by P1, a second position, which is a position on the fused protrusion that is within a distance of ±0.2 mm from the contact line Lb in the width direction and that is farthest from the one end of the ground electrode, is denoted by P2, and a length between the second position P2 and the first position P1 in the longitudinal direction is denoted by Δy, the length Δy satisfies Δ y ≥ 0.1 mm. a center electrode; a ground electrode; and a noble metal tip that has a spark surface facing the center electrode with a spark gap therebetween and that is joined to a part of the ground electrode near one end of the ground electrode via a fused portion, wherein, when the ground electrode, the noble metal tip, and the fused portion are projected in a direction perpendicular to the spark surface, the fused portion extends outward beyond an outer shape of the noble metal tip so that a part of the fused portion is present at each of positions that are located inward from both side edges of the ground electrode and separated from the side edges in a width direction of the ground electrode, and the fused portion includes a fused protrusion that is located near at least one of two side edges of the noble metal tip in the width direction of the ground electrode and that protrudes in a direction away from the one end; wherein, when the ground electrode, the noble metal tip, and the fused portion are projected in the direction perpendicular to the spark surface, and when a maximum tip width of the noble metal tip in the width direction of the ground electrode is denoted by W, a straight line that passes through a center of the noble metal tip and that extends in a longitudinal direction perpendicular to the width direction is denoted by La, a contact line that is in contact with the one of the side edges of the noble metal tip and that extends in the longitudinal direction is denoted by Lb, a first position, which is a position on the fused portion that is within a distance of ±W/4 from the straight line La in the width direction and that is farthest from the one end of the ground electrode, is denoted by P1, a second position, which is a position on the fused protrusion that is within a distance of ±0.2 mm from the contact line Lb in the width direction and that is farthest from the one end of the ground electrode, is denoted by P2, and a length between the second position P2 and the first position P1 in the longitudinal direction is denoted by Δy, the length Δy satisfies Δ y ≥ 0.1 mm.