A controller includes: a low-level error correction section configured to execute low-level error correction in which an error in a code word is corrected with use of a predetermined decoding algorithm; and a high-level soft-decision error correction section configured to execute high-level soft-decision error correction in which the error in the code word is corrected with use of a high-level algorithm when the error correction by the low-level error correction section has failed, the high-level algorithm being a soft-decision decoding algorithm having higher error correction capability than error correction capability of the predetermined decoding algorithm.