Provided are a method and an apparatus for allocating, by a first OFDM system and a second OFDM system, frequency resources, which are multiplexed in a frequency region, in a wireless communication system. Specifically, the sizes of the frequency resources of the first OFDM system, which corresponds to an existing OFDM, and the second OFDM system, which corresponds to a UF-OFDM, are determined. Adjacent subcarriers are instructed to allocate any one of a guard carrier and a subcarrier to which null data is allocated, while performing frequency resource allocation between the first and second OFDM systems in accordance with the determined sizes of the frequency resources. The information regarding the frequency resource allocation, which comprises information indicative of either the guard carrier or the subcarrier, is transmitted.