A spark plug for an internal combustion engine includes a center electrode, a tubular insulator, a tubular metal shell, a ground electrode and an overvoltage preventer. The insulator has the center electrode inserted and held therein. The metal shell has the insulator inserted and held therein such that a proximal part of the insulator is exposed from the metal shell. The ground electrode is joined to a distal end of the metal shell and faces the center electrode through a spark gap formed between the center and ground electrodes. The overvoltage preventer prevents a voltage higher than or equal to a threshold voltage from being applied across the spark gap. The overvoltage preventer is arranged in the proximal part of the insulator so as to be positioned outside the metal shell and farther than the metal shell from the spark gap.