Provided is an air foil journal bearing including a bearing housing; a bump foil disposed inside the bearing housing, having an uneven-shaped elastic bump, having one end coupled and fixed to the bearing housing in the circumferential direction, and having the other end formed as a free end; an outer top foil disposed inside the bump foil; an inner top foil disposed inside the outer top foil; and a middle top foil interposed between the outer top foil and the inner top foil, and coupled and fixed to the bearing housing, thereby preventing deviation of the free end of the bump foil in the width direction due to vibration occurring when a rotor is rotated at a high speed.