An electric power steering system comprising: a housing defining a receiving space therein; a worm shaft which is disposed in the receiving space to be engaged with a worm wheel; a tilt plug which is coupled to the worm shaft which is being inserted into the receiving space to support the worm shaft; and an elastic supporter which is installed to the housing to elastically support the tilt plug toward the worm wheel, wherein the tilt plug is provided with a coupling protrusion which is protruded in an outward direction, and wherein the tilt plug is installed in the housing in a state that the coupling protrusion is inserted into a coupling indentation which is provided to the housing so that a rotation of the tilt plug about a center axis with respect to the housing is restricted, wherein the coupling indentation is formed to allow the tilt plug to move for tilting of the worm shaft by the elastic supporter, wherein the tilt plug comprises: a bearing which is coupled to the worm shaft; a sliding coupling portion which supports the bearing in a direction of a center axis of the tilt plug and is provided with the coupling protrusion formed on one surface thereof to be coupled to an inner surface of the housing; and an elastic ring which encloses an outer circumferential surface of the bearing and is coupled to the sliding coupling portion to fasten the bearing, characterized in that a hooking portion which is bent from an end portion of the elastic ring toward a center axis in a predetermined angle to be hooked to an outer surface of the sliding coupling portion to be supported thereto is formed in the elastic ring, and in that a hooking indentation to which the hooking portion is hooked for fastening is formed in the sliding coupling portion. a housing defining a receiving space therein; a worm shaft which is disposed in the receiving space to be engaged with a worm wheel; a tilt plug which is coupled to the worm shaft which is being inserted into the receiving space to support the worm shaft; and an elastic supporter which is installed to the housing to elastically support the tilt plug toward the worm wheel, wherein the tilt plug is provided with a coupling protrusion which is protruded in an outward direction, and wherein the tilt plug is installed in the housing in a state that the coupling protrusion is inserted into a coupling indentation which is provided to the housing so that a rotation of the tilt plug about a center axis with respect to the housing is restricted, wherein the coupling indentation is formed to allow the tilt plug to move for tilting of the worm shaft by the elastic supporter, wherein the tilt plug comprises: a bearing which is coupled to the worm shaft; a sliding coupling portion which supports the bearing in a direction of a center axis of the tilt plug and is provided with the coupling protrusion formed on one surface thereof to be coupled to an inner surface of the housing; and an elastic ring which encloses an outer circumferential surface of the bearing and is coupled to the sliding coupling portion to fasten the bearing, characterized in that a hooking portion which is bent from an end portion of the elastic ring toward a center axis in a predetermined angle to be hooked to an outer surface of the sliding coupling portion to be supported thereto is formed in the elastic ring, and in that a hooking indentation to which the hooking portion is hooked for fastening is formed in the sliding coupling portion. a bearing which is coupled to the worm shaft; a sliding coupling portion which supports the bearing in a direction of a center axis of the tilt plug and is provided with the coupling protrusion formed on one surface thereof to be coupled to an inner surface of the housing; and an elastic ring which encloses an outer circumferential surface of the bearing and is coupled to the sliding coupling portion to fasten the bearing, characterized in that a hooking portion which is bent from an end portion of the elastic ring toward a center axis in a predetermined angle to be hooked to an outer surface of the sliding coupling portion to be supported thereto is formed in the elastic ring, and in that a hooking indentation to which the hooking