Disclosed is a method for a base station to transmit a downlink control channel in a wireless communication system. Specifically, the method comprises the steps of: determining, on the basis of the number of usable resource elements in one pair of resource blocks, the size of a resource allocation unit for a downlink control channel and the number of resource allocation units within one pair of resource blocks; mapping the downlink control channel, from a preset number of resource block pairs, to the transmission resource on the basis of the determined resource allocation unit; and transmitting the downlink control channel to a terminal, wherein the size of the resource allocation unit is defined by the number of resource elements and is varied according to the number of usable resource elements.