A regular qc matrix is generated in which cyclic permutation matrices with specific regularity are arranged in row and column directions. A mask matrix supporting multiple encoding rates is generated for making the regular qc matrix into irregular. A specific cyclic permutation matrix in the regular qc matrix is converted into a zero-matrix using a mask matrix corresponding to a specific encoding rate to generate an irregular masking qc matrix. An irregular parity check matrix with a LDGM structure is generated, in which the masking qc matrix and a matrix in which the cyclic permutation matrices are arranged in a staircase manner are arranged in a predetermined location.