PURPOSE: To eliminate noise caused by the ruggedness of a disk surface by obtaining a regenerative signal based on a difference of a signal corresponding to a depth of the disk surface from two beams of reflected light separated from two beams of incident light by utilizing a mutual difference in the direction of polarization.
CONSTITUTION: When the disk surface 10 is irradiated with round polarization light, a phase difference is generated by the incident light and the reflected light in accordance with the direction of a magnetic field. Consequently, two beams of round polarization light Lor and Lol rotating right and left are reflected on the disk surface 10 by receiving a phase change in lead phase or lag phase. That is, P-wave is transmitted and S-wave is reflected by a polarization beam splitter (polarization synthesizing and separating means) 5, and two beams of reflected light L' 1 and L' 2 converted into the S-wave and P-wave can be separated by a 1/4-wavelength plate 6. And, since, the reflected light L' 2 (L' 1 ) polarized in the direction at right angle with the incident light L 1 (L 2 ) is formed by the plate 6, the incident light L 1 (L 2 ) and the reflected light L' 1 (L' 2 ) are separated by the splitter 5. Then, since the light of λ 1 in wavelength is transmitted and the light of λ 2 is reflected by dichroic mirrors (wavelength separating means) 4 and 14, the incident light L 1 and L 2 and their respective reflected light L' 2 and L' 1 are separated. Then, the regenerative signal is obtained based on a difference from the signal corresponding to the depth of the disk surface.