A disk drive apparatus is provided that can reproduce data at low bit error rate even if a crosstalk is large. This apparatus comprises means for writing three or more different states of record marks in a read track and adjacent tracks thereof on a disk storage medium, means for detecting read levels of the record marks in the read track, means for calculating every possible read level regarding every possible combination of the record marks in the read track and adjacent tracks thereof according to the detected read levels, and means for performing most-liklihood decoding of written data in accordance with the possible read levels as reference levels.