Spark plug and the metal shell of the spark plug

To provide a better spark plug salt corrosion resistance and stress corrosion cracking resistance. The invention relates to a spark plug having a coated metal shell composite layer containing nickel plating layer and a chromate layer formed on the nickel plating layer, the thickness A of the nickel plating layer, 3 [mu] m ≦ A a ≦ 15 [mu] m, the thickness of the chromate layer B is characterized by a 2 nm ≦ B ≦ 45 nm, the spark plug. .FIELD 4