The present invention relates to a wireless communication system, and more particularly, to a method of transmitting and receiving a radio signal and an apparatus therefor. The method comprises the steps of receiving data in a time unit #n of a first frequency band and transmitting A/N in a time unit #m+k of a second frequency band in response to the data. In this case, the first frequency band and the second frequency band have different subcarrier spacing and a time unit #m of the second frequency band indicates the last time unit among a plurality of time units of the second frequency band corresponding to the time unit #n of the first frequency band.