SPARK PLUG

In a spark plug including an electrode having a cover portion and a core portion, the occurrence of a gap between the cover portion and the core portion is suppressed. In a spark plug including a center electrode and a ground electrode that forms a gap between the center electrode and the ground electrode, at least one of the center electrode and the ground electrode has a cover portion and a core portion covered with the cover portion and formed of a material having a thermal expansion coefficient different from that of the cover portion. The core portion of the at least one electrode has a concave portion and a convex portion formed at the front end thereof. The convex portion is such that, in a cross section passing through the barycenter of the front surface of the electrode and also passing through the convex portion, the area of the convex portion delimited by a line perpendicular to the bisector of the convex portion and passing through a point 0.2 mm shifted from the front end of the convex portion in the direction of the bisector is smaller than the area of a triangle formed by connecting the front end of the convex portion and intersections of the line perpendicular to the bisector and the contour of the convex portion.