PURPOSE: To improve recording density by reducing a beam diameter of a laser beam in the peripheral direction of a disk than the beam diameter in the radial direction in the case of irradiating a laser beam a glass original disk and forming uneven cross-sectional shapes.

CONSTITUTION: The laser beam from a laser light source 1 is divided to two directions by a polarizing beam splitter 2. One side exposes a groove part passing through an optical modulator 5. The other side, after passing through the optical modulator 4, passes through a beam shape converter 6 and exposes parts of an address signal, etc., and a ROM area. By the converter 6, the spot shape of the laser beam exposing the part of the address signal, etc., is changed, and the beam diameter in the peripheral direction of the disk is reduced than the beam diameter in the radial direction of the disk. These modulated two pieces of laser beams are synthesized by the polarizing beam splitter 8, and are converged on a photoresist 11 on the glass original disk 12 as two spots by a condenser lens 10. Thus, recording density in the longitudinal direction of the track is increased.