a recording part iteratively recording the data at a data unit dividing the data by a predetermined data length on predetermined recording areas on a recording medium;

a plurality of storage sample value storing parts corresponding to the predetermined recording areas, respectively, each storage sample value storing part storing a sample value obtained by sampling a regenerative signal from the data recorded on each recording area at the data unit;

a plurality of pass metric calculating parts corresponding to said plurality of storage sample value storing parts, respectively, each pass metric calculating part calculating a branch metric and a pass metric based on each sample value;

a plurality of likelihood converting parts corresponding to said plurality of pass metric calculating parts, respectively, each likelihood converting part converting a calculation result obtained by each said pass metric calculating part into likelihood of the calculation result,

wherein said each pass metric calculating part calculates the pass metric based on the likelihood converted by one of said other likelihood converting parts and decodes the data recorded on the recording medium, and

said each likelihood converting part converts the calculation result based on a pass metric difference between metric values “0” and “1”.