Disclosed is a communication method in a multi-carrier system, including: allocating radio resources for transmitting signals to a middle guard band; and transmitting the signals through the radio resources; wherein the middle guard band is a frequency band positioned between used bands of a plurality of carriers, respectively, within an aggregated carrier formed by aggregating the plurality of carriers and a unit allocating the radio resources of the middle guard band is different from a unit allocating the radio resources of the used bands. A multi-carrier system uses the guard bands between the carriers to improve channel estimation performance or increase efficiency of radio resources.