A method of transmitting cyclic prefix length information when wireless access systems having different cyclic prefix lengths coexist is disclosed. The method of transmitting cyclic prefix length information comprises including the cyclic prefix length information in a preamble; and transmitting the preamble to a receiving end, whereby a transmitter can notify the receiving end of a current cyclic prefix length. Also, in a specific interval where a super frame header is defined, a single cyclic prefix length is used in a legacy support mode and a legacy disable mode, and cyclic prefix length information of other data or control channel is included in the super frame header and then transmitted to the receiving end. If different CP lengths are used in a legacy support mode of an evolved system, it is possible to solve a problem in detecting a control channel or a data channel, which may occur as the CP lengths are not distinguished from each other after preamble detection.