A spark plug including a metallic shell having a ground electrode, an insulator held inside the metallic shell and having an axial hole having a small diameter portion, an intermediate diameter portion connected to a rear end of the small diameter portion via a step portion, and a large diameter portion disposed on the rear side of the intermediate diameter portion, a resistor disposed inside the large diameter portion, a center electrode having a flange portion which bulges in a radial direction inside the intermediate diameter portion and comes into contact with the step portion and a leg portion which extends forward from the flange portion and is disposed inside the small diameter portion, and a seal disposed on the rear side of the step portion and electrically connecting the center electrode and the resistor. The rear end of the seal is located inside the intermediate diameter portion.