PURPOSE: An uplink ACK/NACK timing adjustment for changing ACK/NACK transmission timing in a synchronization method is provided to efficiently control the transmission timing of uplink ACK/NACK signal in a relay system. CONSTITUTION: A terminal obtains ACK/NACK transmission timing for transmitting synchronization ACK/NACK(S1410). The terminal receives downlink data(S1420). The terminal generates ACK/NACK after decoding downlink data(S1430). The terminal performs the UL(UpLink) transmission of ACK/NACK after passing from a downlink data reception point(S1440).
