The present invention relates to a wireless communication system and, specifically, to a method comprising the steps of: transmitting first A/N information; receiving one or more data after transmitting the first A/N information; receiving downlink control information including a 1-bit indicator; and transmitting second A/N information including an A/N result for the one or more data depending on whether the 1-bit indicator is toggled, and to an apparatus therefor, wherein the second A/N information is generated by reflecting only a data reception state after the transmission of the first A/N information, on the basis of a case where the 1-bit indicator has been toggled; and the second A/N information is generated in consideration of (i) the first A/N information and (ii) the data reception state after the transmission of the first A/N information, on the basis of a case where the 1-bit indicator has not been toggled.