The present invention relates to a wireless communication system. In more detail, in relation to a method for a terminal to transmit ACK/NACK in a wireless communication system, an ACK/NACK transmission method includes: receiving at least one Physical Downlink Shared Channel (PDSCH); transmitting at least one ACK/NACK corresponding to the at least one PDSCH through a plurality of Physical Uplink Control Channel (PUCCH) formats; and, when the at least one ACK/NACK is transmitted using a first PUCCH format, transmitting at least one ACK/NACK in an antenna port transmission mode set for a second PUCCH format.