An apparatus for data transmission is provided. The apparatus includes a data processor encoding an information bit and generating a modulation symbol by performing constellation mapping on the encoded information bit, a discrete Fourier transform (DFT) unit performing DFT on the modulation symbol to generate a frequency-domain symbol, a space time block coding (STBC) processor performing STBC on the frequency-domain symbol to generate an STBC code consisting of 1st and 2nd STBC streams, a subcarrier mapper mapping the 1st STBC stream to a 1st subcarrier and mapping the 2nd STBC stream to a 2nd subcarrier, an inverse fast Fourier transform (IFFT) unit performing IFFT on the 1st subcarrier to generate a 1st single carrier-frequency division multiple access (SC-FDMA) symbol and performing IFFT on the 2nd subcarrier to generate a 2nd SC-FDMA symbol, and a plurality of transmit antennas transmitting the 1st and 2nd SC-FDMA symbols. STBC is effectively applied to a SC-FDMA system to decrease a peak-to-average power ratio (PAPR) and to maintain a single-carrier property.