The present invention relates to a wireless communication system. Specifically, the present invention relates to a method of transmitting an uplink signal in a state in which a PUSCH sub-frame bundling mode is set, including the steps of: receiving a first PDCCH signal having an uplink grant through a first downlink sub-frame; receiving a second PDCCH signal having an uplink grant through a second downlink sub-frame: and one or more continuous uplink sub-frames of a predetermined size transmitting a PUSCH signal corresponding to the second PDCCH signal when a value corresponding to an interval between the first downlink sub-frame and the second downlink sub-frame is smaller than a bundling size set through a higher layer, wherein the predetermined size is set as the size smaller than the bundling size, and an apparatus therefor.