A method for modifying a synchronous non-adaptive retransmission scheme to solve the limitation of the synchronous non-adaptive retransmission scheme is disclosed. A method for indicating not only the new data transmission but also the retransmission using a data scheduling message is disclosed. A method for determining whether there is an error in the ACK signal transmitted from a data reception end using another message to-be received later is disclosed. The retransmission method for a multi-carrier system includes: receiving a grant message including scheduling information for transmitting uplink data wherein a retransmission scheme for the uplink data is predetermined by a first retransmission scheduling, transmitting the uplink data according to the scheduling information and retransmitting the uplink data according to second retransmission scheduling by receiving the second retransmission scheduling information associated with the uplink data with retransmission request.