In a slew rate limiter, a slew rate is limited so as not to pass a signal varying more abruptly than a wobble signal included in a difference signal generated by a differential amplifier, and this limited slew rate is used to process the difference signal to be outputted. That is, the slew rate limiter removes a signal varying more abruptly than a wobble signal included in a difference signal DIFO, and then outputs only the wobble signal. A DAC generates an offset voltage. An adder is used to add this offset voltage to the wobble signal from the slew rate limiter. The signal obtained by this addition as a slice level is compared by a comparator with the difference signal, thereby reproducing an LPP signal.