A method and apparatus for transceiving additional data using unallocated slots of a header of a frame used in a broadcast system are provided. A data transceiving apparatus includes a data transmitter for encoding, modulating, and transmitting a broadcast frame including a first region containing broadcast data and a second region containing additional data and a data receiver for receiving the broadcast frame, extracting at least any of the broadcast data and the additional data from the broadcast frame, and processing the broadcast data and the additional data independently.