The present invention relates to a broadband wireless access system, and more particularly, to a frame structure to which OFDM symbols having a cyclic prefix are transmitted. A method of constructing a frame in a broadband wireless access system according to one embodiment of the present invention comprises including one or more first subframes in the frame, the first subframes including a plurality of symbols having a cyclic prefix of a first length; and including one or more second subframes in the frame, the second subframes including a plurality of symbols having a cyclic prefix of a second length different from the first length, wherein the number of the first subframes and the number of the second subframes are determined considering an idle time for which effective symbols are not included in the frame.