The present invention relates to a wireless communication system. More particularly, the present invention relates to a method in which a terminal transmits control information in a CA-based wireless communication system and to an apparatus for the method, the method comprising: a step of configuring a first cell and a second cell having different subframe configurations, the second cell has UL-DL configuration #0; a step of receiving a downlink control information (DCI) format including an N-bit field (N>1), for the second cell; and a step of transmitting a physical uplink shared channel (PUSCH) signal corresponding to the downlink DCI format through a subframe. The N-bit field indicates either an uplink (UL) index or a downlink assignment index (DAI). For PUSCH timing, in cases where a reference UL-DL configuration applied to the second cell is any one of UL-DL configurations #1 to #6, the N-bit field indicates the DAI.