Impact attenuator

An impact attenuator includes: a plurality of support frames installed in a row at an interval, each support frame having first and second horizontal beams, a reinforcing member installed between the first and second horizontal beams, and at least one wire clip installed under the first horizontal beam; a rear support integrally formed with one of the support frames and having a vertical beam; a plurality of guard rail connecting units, each guard rail connecting unit including guard rails installed on opposite sides of each of the support frames and a fixing member for movably installing the guard rails; and an absorbing tank including a front tank installed on a front surface of one of the support frames and a plurality of cushion tanks installed between the support frames, wherein a wire rope connects the support frames and the rear support to guide linear movements of the support frames.