Spark plug

A spark plug comprising a center electrode and a ground electrode which forms a gap between the ground electrode and the center electrode,

• wherein, when a side toward the gap is taken as a front side of the center electrode or 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 a thermal expansion coefficient of the cover portion,
• the core portion of the at least one electrode has a concave portion and a convex portion formed at a front end thereof, and
• the convex portion is such that, in a cross section passing through a barycenter of a front surface of the electrode and also passing through the convex portion, an area of the convex portion delimited by a line perpendicular to a bisector of the convex portion and passing through a point 0.2 mm shifted from a front end of the convex portion in a direction of the bisector is smaller than an area of a triangle formed by connecting the front end of the convex portion and intersections of the line perpendicular to the bisector and a contour of the convex portion.