A data converting means generates first interim data held in one-to-one correspondence to columns vectors from data stored in a first storage means and data stored in a second storage means. A check node processing means generates second interim data for updating the data stored in the first storage means based on the sum of the first interim data and received data. The data converting means updates the data stored in the second storage means using the first interim data, and updates the data stored in the first storage means using the second interim data generated by the check node processing means. Decoded data are generated by a process carried out by the data converting means and the check node processing means.