At a preceding stage of a PR-channel APP decoder out of two APP decoders constituting a turbo decoder is disposed a logarithmic-likelihood computing circuit that computes logarithmic likelihoods L(y′i|yi) of a reproduced signal y′i, which is soft information. At a succeeding stage of the PR-channel APP decoder, on the other hand, a likelihood-transform RLL demodulator and a likelihood-transform RLL modulator capable of treating logarithmic likelihood ratios, which are soft information, are disposed between this APP decoder and a convolutional-code APP decoder. Thus, both RLL demodulation and turbo decoding can be fulfilled, and a turbo decoding of high error-correcting capability can be used to reproduce channel data ai recorded on a recording medium. As a result, the recording density of the recording medium is enhanced.