An ACK/NACK (acknowledgement/negative-ACK) transmission method in a wireless access system that supports device-to-device communication and an apparatus therefor are disclosed. Specifically, a method for transmitting ACK/NACK in a wireless access system that supports the device-to-device communication comprises the steps of: receiving first data in a first sub-frame, receiving second data from a base station in a second subframe, and when data transmission and reception through the device-to-device communication carried out in a third sub-frame for transmitting the ACK/NACK information on the first data, transmitting, to the base station in a fourth sub-frame, a grouped ACK/NACK information including the ACK/NACK information on the first data and the ACK/NACK information on the second data.