Abstract: A DVD-ROM data decoding processing system includes a DVD-ROM reproducing unit 32 and a buffer memory 34. The DVD-ROM reproducing unit 32 includes a demodulating part 36, a PI syndrome generating part 38, an error correcting part 40, a buffer memory 42 having a memory capacity corresponding to a few lines, a PO syndrome generating part 44, a descrambling/EDC calculating part 46, a PI syndrome storing memory 48, a PO syndrome storing memory 50, an EDC calculation result storing memory 52, an error correcting part 54, and a CPU 56. The error correcting part 40 derives the position and the magnitude of errors in the PI series from the PI syndromes generated in the PI syndrome generating part 38, and corrects the data errors in the buffer memory 42 on the basis of the position and the magnitude of errors in the PI series, interleave by interleave.