A rack assist type power steering apparatus according to the embodiments of the present disclosure comprises a rack bar provided with an outer screw groove on an outer circumferential surface, a ball nut having an inner screw groove corresponding to the outer screw groove on an inner circumferential surface, and a bearing coupled to an outer circumferential surface, and a nut pulley provided with a belt coupling portion on an outer peripheral surface, and one end of an inner circumferential surface is provided with a support end coupled to an outer circumferential surface of the ball nut to support the bearing, and an other end of an inner circumferential surface is provided with an enlarged diameter portion which is stepped from the support end and increases in inner diameter.