A method of retransmitting data by using a parity check matrix for low density parity check, LDPC, code, the method comprising: encoding an input data stream using a first sub-matrix of a parity check matrix including a plurality of sub-blocks having a size of z-by-z; transmitting the input data stream encoded by the first sub-matrix to a receiving side; receiving a response signal from the receiving side in response to the transmitted input data stream; encoding the input data stream using a second sub-matrix of the parity check matrix if the received response signal is a negative acknowledgement, NACK; and transmitting the input data stream encoded by using the second sub-matrix, wherein the first sub-matrix and the second sub-matrix include a predetermined number of sub-blocks among the plurality of sub-blocks, and the first sub-matrix is a sub-matrix of the second sub-matrix, wherein the parity check matrix is divided into a systematic part and a parity part, and the systematic and parity parts of the parity check matrix consist of a plurality of sub-blocks each of which is a z-by-z zero matrix, a z-by-z identity matrix or a z-by-z permutation matrix generated by right shifting each row of the z-by-z identity matrix as much as a positive integer, wherein the parity part of the parity check matrix is a lower triangle type matrix in which each sub-block on a main diagonal and an adjacent diagonal located lower than the main diagonal is the z-by-z identity matrix, wherein the first sub-matrix is divided into a first systematic part and a first parity part, and the second sub-matrix is divided into a second systematic part and a second parity part, wherein the first systematic part of the first sub-matrix and the second systematic part of the second sub-matrix have the same number of columns as the systematic part of the parity check matrix, and wherein the last column in each of the first parity part of the first sub-matrix and the second parity part of the second sub-matrix includes an odd number of sub-blocks other than the z-by-z zero matrix, wherein the odd number is not less than two. encoding an input data stream using a first sub-matrix of a parity check matrix including a plurality of sub-blocks having a size of z-by-z; transmitting the input data stream encoded by the first sub-matrix to a receiving side; receiving a response signal from the receiving side in response to the transmitted input data stream; encoding the input data stream using a second sub-matrix of the parity check matrix if the received response signal is a negative acknowledgement, NACK; and transmitting the input data stream encoded by using the second sub-matrix, wherein the first sub-matrix and the second sub-matrix include a predetermined number of sub-blocks among the plurality of sub-blocks, and the first sub-matrix is a sub-matrix of the second sub-matrix, wherein the parity check matrix is divided into a systematic part and a parity part, and the systematic and parity parts of the parity check matrix consist of a plurality of sub-blocks each of which is a z-by-z zero matrix, a z-by-z identity matrix or a z-by-z permutation matrix generated by right shifting each row of the z-by-z identity matrix as much as a positive integer, wherein the parity part of the parity check matrix is a lower triangle type matrix in which each sub-block on a main diagonal and an adjacent diagonal located lower than the main diagonal is the z-by-z identity matrix, wherein the first sub-matrix is divided into a first systematic part and a first parity part, and the second sub-matrix is divided into a second systematic part and a second parity part, wherein the first systematic part of the first sub-matrix and the second systematic part of the second sub-matrix have the same number of columns as the systematic part of the parity check matrix, and wherein the last column in each of the first parity part of the first sub-matrix and the second parity part of the second sub-matrix includes an odd number of sub-blocks other than the z-by-z zero matrix, wherein the odd number is not less than two.