A spark plug includes a center electrode, a ground electrode formed of a metal material containing 95% or more of nickel and a substantially cylindrical metal shell having a front end face to which one end of the ground electrode is welded. In the spark plug, the conditions: 0.15 mm≦BD≦0.40 mm; and (EW2−EW1)/EW1≧0.1 are satisfied where BD is a depth from the front end face of the metal shell to a portion of the ground electrode embedded most deeply in the metal shell; EW1 is a width of a portion of the ground electrode located closest to a portion of the ground electrode deformed by the welding; and EW2 is a width of the portion of the ground electrode deformed by the welding at the front end face of the metal shell.