1. A decoding method for LDPC (Low Density Parity Check) codes, which is for decoding a LDPC codeword encoded with LDPC codes, the decoding method comprising: (a) dividing nodes into check nodes for a parity-check message and variable nodes for a bit message according to a parity-check matrix; (b) dividing the check nodes into a predetermined number of subsets; (c) sequentially decoding the LDPC codeword of each subset for all the check nodes; (d) generating an output message for verifying validity of the decoding result; and (e) iteratively performing the steps (b), (c), and (d) by a predetermined number of iterations.