The invention provides a decoding method and a decoding device that can approximate a row arithmetic operation based on a Sum-Product decoding method with a high degree of precision by using an Offset BP-based decoding method, thereby improving the performance of decoding of an error correcting code. In row calculation, a value which is obtained by subtracting an offset according to a minimum of the absolute values of column LLRs from the minimum of the absolute values of the column LLRs is set as a row LLR corresponding to a column of the column LLRs.