The metallic shell of a spark plug has an enhanced insulator retaining performance. The spark plug includes a ceramic insulator having a generally tubular shape and a through hole extending in the axial direction, the ceramic insulator having a center electrode on a forward end side of the through hole in the direction of the axial line. The spark plug also includes a metallic shell formed in a generally cylindrical shape and having a crimp portion at a rear end of the metallic shell in the axial direction, the crimp portion being crimped in a state in which the ceramic insulator is inserted into the metallic shell so that the ceramic insulator is held by the metallic shell. The crimp portion satisfies a relation of A ‰¥ 1.7 mm and a relation of t ‰¥ 1.20 mm in a cross section of the crimp portion taken along a plane containing the axial line, where A is the distance between a closest point which is a point within the cross section closest to the ceramic insulator and an intersection at which a first orthogonal line passing through the closest point and orthogonal to the axial line intersects with an outer circumference of the crimp portion, and t is a thickness of the proximal end of of the crimp portion.