A spark plug includes: a cylindrical mounting bracket attachable to an internal combustion engine; a center electrode that is held by the mounting bracket in an insulated manner and has a first end portion exposed and extended from a first end portion of the mounting bracket; a ground electrode that has a first end side joined to the first end portion of the mounting bracket and has a surface of the second end side extended to be opposed to the first end portion of the center electrode; a convex portion that protrudes from a base material of the ground electrode on the surface of the ground electrode toward the center electrode, has a surface protruded outward, and has surfaces without corners; and a precious metal layer formed on the surface of the convex portion.