1. An error correction encoding method of calculating a parity bit sequence from an information bit sequence by using a sparse parity-check matrix for QC (Quasi-Cyclic)-LDPC (Low-Density Parity-Check) codes, and encoding the parity bit sequence, said error correction method comprising: a sparse matrix computing step of computing exclusive OR of submatrices, in said sparse parity-check matrix, corresponding to said information bit sequence on a basis of a position of 1 in each of said submatrices to calculate a plurality of vectors; a vector element summing step of acquiring a vector which is a sum of said plurality of vectors acquired in said sparse matrix computing step; a first matrix multiplying step of multiplying an inverse matrix of a matrix which is acquired by summing up a part of submatrices, in said parity-check matrix, corresponding to said parity bit sequence and said sum vector acquired in said vector element summing step to calculate a part of said parity bit sequence; a second matrix multiplying step of multiplying said part of the submatrices which is the target for the summation in said first matrix multiplying step and the part of said parity bit sequence acquired in said first matrix multiplying step to acquire a vector which is a multiplication result; and a parity bit calculating step of calculating a remaining part of said parity bit sequence on a basis of said plurality of vectors acquired in said sparse matrix computing step and said vector which is the multiplication result acquired in said second matrix multiplying step.