The objective of this invention is to perform high-precision tracking error detection and tracking control using digital circuitry at relatively low speed and with a small circuit scale. Tracking servo circuit is formed as a single-chip circuit. Low-pass filters (LPF) and gain control amplifiers (GCA) of the input portion are analog circuits, while the circuits after analog-digital (A/D) converters, that is, offset cancellation circuits, equalizers (EQ), first and second phase difference detectors, adder, low-pass filter (LPF), gain control amplifier (GCA), and servo DSP are all digital circuits.