PURPOSE: To realize a verifying function, an overwriting function, etc., by converging reflected light from a disk into two optical spots again by a converging means and then splitting into two luminous fluxes through a space filter.
CONSTITUTION: Divergent light beams from semiconductor lasers 1a, 1b are converted into parallel light beams through collimator lenses 2a, 2b, transmitted through half mirrors 3a, 3b and then condensed on the surface of a track on a disk 5 as optical spots A1, B1 through an objective lens 5. Reflected light beams from the disk 5 are transmitted in the reverse course, reflected by a half mirror 3b and converged into optical spots A2, B2 through a convex lens 6. The optical spot B2 is shielded by a space filter 7a having a fine pin hole and only the light beams of the optical spot A2 are made incident upon a signal detecting means 8a to detect a focus error signal, a tracking error signal and an information signal. Since the verifying function, the overwriting function, etc., can be obtained with a simple constitution, chromatic aberration due to using a semiconductor laser with the same wavelength is not generated.