An error correction encoding apparatus wherein the apparatus structure is simple; an iterative decoding is used to achieve a decoding with a close-to-optimum precision; and a simple mathematical expression is used to perform an evaluation of the characteristic of an error floor area without using any computer experiments. In a polynomial multiplying block 1, (n−1)-th-order polynomial multiplying units (12-1 to 12-(m−1)) further divide an information bit string, which has been blocked for an error correction encoding, into (m−1) blocks having a length n and a single block having a length (n-r) (where m and n represent integers equal to or greater than two and where r represents an integer between 1 and n inclusive); receive blocks, which have the length n, of divided information bit strings; and output a series having the same length. An r-th-order polynomial dividing unit 2 receives an addition of the outputs from the respective (n−1)-th-order polynomial multiplying units (12-1 to 12-(m−1)) and also receives a block having the length (n-r), and outputs a redundant bit series having a length r.