A spark plug includes a center electrode, an insulator, a metallic shell, and a ground electrode which has a noble metal tip at the other end portion. A gap is formed between a forward end portion of the center electrode and a discharge surface of the noble metal tip. When an acute angle formed by the forward end surface and the discharge surface is θ1, a point on the forward end surface closest to the noble metal tip is A, opposite ends of the discharge surface are B1 and B2, and an angle formed by a first line segment connecting A and B1 and a second line segment connecting A and B2 is θ2, 35°≦θ1≦55°, 85°≦θ2≦90°, and the difference in length between the first and second line segments is equal to or less than 10% of the longer line segment.