a laser oscillation circuit for generating laser light for recording/playback of digital data in/from an optical recording medium in which address information exists intermittently, and wobbles are carved along recording tracks;

a first photodetector for detecting reflected light of the laser light from the optical recording medium, as four light signals into which the reflected light is divided along a track direction axis that is a digital data recording direction, and a radius direction axis that is perpendicular to the track direction axis;

a light difference signal detection circuit for, among the tour outputs from the first photodetector which have been subjected to currently-to-voltage conversion, adding the outputs from two areas parallel to the track direction axis, and adding the outputs from the other two areas parallel to the track direction axis, and detecting a difference between the respective addition values to output a light difference signal;

a second photodetector for detecting a focus error signal, which detects the reflected light of the laser light from the optical recording medium as a light signal that is divided into two along the radius direction axis that is perpendicular to the track direction axis;

a playback signal detection circuit for detecting a playback RF (Radio Frequency) signal by using either the output of the first photodetector which has been subjected to current-to-voltage conversion or the output of the second photodetector which has been subjected to current-to-voltage conversion, or using both of the output of the first photodetector which has been subjected to current-to-voltage conversion and the output of the second photodetector which has been subjected to current-to-voltage conversion;

an optical disc controller for transmitting/receiving data and commands to/from an external device, and controlling recording and playback in/from the optical recording medium;

a recording gate signal generation circuit for generating a recording gate signal which indicates either a recording state indicating recording of the digital data or a playback state indicating playback of the digital data or the address information, on the basis of a command from the optical disc controller;

a light difference signal shaping circuit for output two signals by performing different adjustments to the light difference signal on the basis of the different states indicated by the recording gate signal;

a clock generation circuit for generating a sampling clock that is synchronized with a clock component included in the playback signal of the optical recording medium, from one of the output signals of the light difference signal shaping circuit;

a first analog-to-digital converter for converting the other output signal of the light difference signal shaping circuit into a digital sampling signal, by the sampling clock;

an address information preprocessing circuit for converting the digital sampling signal into an address information preprocessing signal for detecting the address information;

a wobble amplitude information preprocessing circuit for converting the digital sampling signal into a wobble amplitude information preprocessing signal for detecting wobble amplitude information as amplitude information of the wobbles;

an address information detection circuit for detecting address information from the address information preprocessing signal;

a wobble amplitude information detection circuit for detecting wobble amplitude information from the wobble amplitude information preprocessing signal;

a recording laser power control circuit for controlling a laser power generated by the laser generation circuit, during recording of digital data, in synchronization with variations in the wobble amplitude information, so that the quality of recorded data is appropriately maintained; and

a digital data reproduction circuit for demodulating digital data from the playback RF signal on the basis of the sampling clock to obtain a binarized digital signal, and outputting the binarized digital signal to the optical disc controller.