A spark plug including a metal shell having a ground electrode, a cylindrical ceramic insulator held in the metal shell and having therein an axial hole having a small-diameter portion, and a large-diameter portion larger in diameter than the small-diameter portion and connected to a rear end of the small-diameter portion via a stepped portion, a resistor arranged in the large-diameter portion, a center electrode having: a flange portion projecting in a radial direction in the large-diameter portion to contact with the stepped portion; and a leg portion arranged in the small-diameter portion so as to extend from the flange portion toward the front end side, and a seal body arranged in the large-diameter portion and electrically connecting between the center electrode and the resistor. The seal body includes an insulating seal body that comes into contact with the ceramic insulator, and a conductive seal body.