Abstract: When an information length N is divided by a division length L, if the number of divisions including the remainder is 2n, then backward probabilities are calculated from the Nth backward probability in the reverse direction to the (n+1)th section and backward probabilities at division points are stored as discrete values, and in parallel with these backward probability calculations, forward probabilities are calculated from the first forward probability in the forward direction to the nth section and the forward probabilities at division points are stored as discrete values. Subsequently, the backward probabilities and forward probabilities stored as discrete values are used to calculate backward probabilities and forward probabilities for each section, and using these probabilities, decoding results are calculated in sequence for all sections.