Disclosed herein is an air foil bearing capable of adjusting stiffness of single bumps by varying widths of the single bumps. Since the bumps have the same height in an initial stage, a wedging effect is implemented only when a load is applied thereto by an oil film. Therefore, the air foil bearing is advantageous in terms of height management thereof. In addition, it is possible to stably dampen shocks applied in the direction of rotation of a rotor, to improve a support capability, and to reduce shocks due to damping. Therefore, it is possible to enhance durability of the air foil bearing.