In a slew rate limiter, a slew rate is limited in such a manner that passage of a signal which changes more steeply than a wobble signal included in a differential signal generated in a differential amplifier can be prevented, and the differential signal is processed with the slew rate so as to be outputted. That is, a signal which changes more steeply than the wobble signal included in the differential signal DIFO is removed, thereby enabling only the wobble signal to be outputted from the slew rate limiter. An offset voltage which is generated by a DAC, is also added by an adder to the wobble signal from the slew rate limiter and thereafter the differential signal is compared in a comparator with the addition signal as a slice level, for reproducing a LPP signal.