According to one embodiment, a data reproducing apparatus includes a reader, Viterbi decoder, metric difference calculator, an error correction decoder, and a detector. The reader reads data. The Viterbi decoder decodes the data read by the reader. The metric difference calculator calculates a metric difference between a maximum likelihood path and a competitive path, based on an output from the Viterbi decoder. The error correction decoder executes an error correction decoding for the output of the Viterbi decoder. The detector detects that an error detected by the error correction decoder is uncorrectable, and the metric difference detected by the metric difference calculator is larger than a predetermined value.