The present invention relates to a variety of hybrid automatic repeat request (HARQ) methods, data buffering methods therefor, and apparatuses supporting the methods, in a wireless access system supporting a non-orthogonal multiple access (NOMA) scheme. As one embodiment of the present invention, a data buffering method, by a first terminal, for hybrid automatic repeat request (HARQ) in a wireless access system supporting a non-orthogonal multiple access (NOMA) scheme may comprise: a step of receiving, from a base station, data in which data for the first terminal and a second terminal are multiplexed in a NOMA scheme; a step of decoding the multiplexed data; a step of buffering data for the second terminal; and a step of transmitting HARQ-ACK information to the base station, depending on the decoding result.