Patent ID: 8704435

Claim:
A spark plug comprising: a cylindrical housing case; a cylindrical glass insulator supported by an inside of the cylindrical housing case; a center electrode supported in the inside of the cylindrical glass insulator so that a front part of the center electrode is exposed toward the outside of the spark plug; and an earth electrode fixed to the cylindrical housing case, wherein: the earth electrode has a projected part projected toward the center electrode, the projected part of the earth electrode has a facing surface which faces the center electrode and is closest to a front part of the center electrode in a spark discharge gap, the spark discharge gap is formed between the center electrode and the earth electrode, and the facing surface of the projected part of the earth electrode is covered with a plating layer, and a base material, with which the earth electrode is made, is exposed on a side surface of the projected part around the facing surface of the projected part of the earth electrode; and the plating layer is made of Ni, and the base material of the earth electrode is made of Ni alloy containing not less than 90 wt % Ni.