A data transmission apparatus in a communication system includes a reception unit configured to receive terminal information from a plurality of terminals through a new frequency band for transmission and reception of data between the plurality of terminals and an AP (access point); a determination unit configured to determine access timing of the terminals to the AP by using the terminal information, and generate terminal access information including information on the access timing; and a transmission unit configured to transmit the terminal access information and beacon frames to the terminals, wherein the terminals access the AP and transmit data frames to the AP, at the access timing based on the beacon frames.