According to one embodiment, a method for operating log likelihood ratios in a disk apparatus is disclosed. Iterative decoding is applied to the disk apparatus. The method can set windows for a sequence of the log likelihood ratios output by a soft-decision most-likelihood decoder based on the sequence of the log likelihood ratios or an amplitude of a read signal acquired in response to read of data from a data sector on a disk carried out by a head. The method can multiply the log likelihood ratios contained in each of the windows, by a multiplier specific to each window. In addition, the method can transmit the sequence of the log likelihood ratios multiplied by the multiplier for each of the windows to a parity check decoder.