An air bag is configured to be miniaturized by a foldable structure of an air bag cushion in a driver seat and to safely protect a driver by enlarging a protection area thereof, and the air bag includes a first folded part configured to be folded in a vertical direction of an air bag cushion, and wherein the first folded part is unfolded in deployment to increase a vertical length of the air bag cushion, and a second folded part configured to be folded in leftward and rightward directions of the air bag cushion, and wherein the second folded part is unfolded in deployment to increase a transverse length of the air bag cushion.