Provided are a method and device for transmitting control information in a wireless communication system. In particular, a downlink resource block group including a downlink resource block in a downlink frequency bandwidth is set, and an uplink resource block group including an uplink resource block in an uplink frequency bandwidth is set. If the downlink frequency bandwidth is smaller than the uplink frequency bandwidth, the downlink resource block group is mapped to the uplink resource block group. The ratio of the number of uplink resource blocks to the number of downlink resource blocks is set so that the number of uplink resource block groups and the number of downlink resource block groups become the same. The uplink and downlink resource block groups are mapped according to the ratio. Control information on the mapping is transmitted through the downlink resource block groups.