The spark plug includes a cylindrical insulator, a center electrode provided in the insulator, and a cylindrical metal shell provided around the insulator. A ledge portion of the metal shell has a frontward facing surface facing a front side, a rearward facing surface facing a rear side, and a connection surface connecting the rearward facing surface and the frontward facing surface. The rearward facing surface engages with a step portion of the insulator. The metal shell includes a front cylindrical portion connected to the front side of the ledge portion. The inner circumferential surface of the front cylindrical portion is connected to the frontward facing surface of the ledge portion via a chamfered surface or a rounded surface. A corner at which the connection surface and the frontward facing surface are connected is located on the front side with respect to a front end of the insulator.