Abstract: An air foil bearing includes a bearing housing having a cylindrical shape that forms an accommodation space in a middle thereof for a rotating shaft, rotor, or journal; a first foil including a plurality of bump foils, which are arranged along an inner wall surface of the accommodation space of the bearing housing; and a second foil including a plurality of top foils, which are arranged in a circumferential direction along an inner circumference of the bearing housing to correspond to the plurality of bump foils and to support the rotating shaft, rotor, or journal. A portion of at least one of the plurality of top foils of the second foil is thicker than the other top foils of the plurality of top foils.