The generation of a pseudo-lock is prevented in a JFB offset compensator whose use has been conventionally limited due to a tendency to generate the pseudo-lock, and performance degradation of a PLL and a Viterbi decoder is suppressed. A means for monitoring an offset of a read signal is provided independently from the JFB offset compensator. With this configuration, the generation or a possibility of the generation of the pseudo-lock can be detected to reset an integrator. In order to reduce the influence of a large sporadic offset triggering the pseudo-lock, there may also be provided a limitter for limiting the absolute value of an offset signal inputted to the integrator or a limitter for limiting the absolute value of an offset compensation signal.