As an embodiment of the present invention, a method for supporting a HARQ operation of M2M devices using a HARQ Channel Identifier (ACID) in a wireless access system includes transmitting, at a base station, a second UL A-MAP IE to M2M devices sharing a station identifier (STID) in a subframe in which a second M2M device is to retransmit a UL burst, wherein the second UL A-MAP IE includes resource allocation information for allocating a resource region to a first M2M device and includes a second ACID, receiving the UL burst retransmitted using a first ACID from the second M2M device in the subframe, and receiving a new UL burst transmitted using the second ACID from the first M2M device in the subframe, wherein the first and second M2M devices share the STID, and the first and second ACIDs are different from each other.