A method of transmitting a wideband frame for a wideband system having backward compatibility with a narrowband system includes configuring a wideband carrier by using a set of base carriers, wherein a bandwidth of the base carriers corresponds to a bandwidth of the narrowband system and any one of center frequencies of the base carriers is the same as a center frequency of the narrowband system, and allocating all or some of guard subcarriers between the two adjacent base carriers to a traffic channel when a center frequency spacing between two adjacent base carriers is an integer multiple of a subcarrier spacing. Accordingly, the method can be used to support backward compatibility with the narrowband system. Further, the method can be equally used when the narrowband system co-exists with the wideband system in a guard band defined in a narrowband of a new system.