PURPOSE: To provide a method for generating optical information by which a device is made compact and high-reliable optical information can be generated without using a shielding plate.

CONSTITUTION: Plural electrode wires 10 are arranged on an electrooptical crystal 8 and the phase of luminous flux passed through a gap between the respective electrode wires 10 is spatially modulated by the wires 10. Besides, one part of light distribution expanded by the diffraction of the luminous flux whose phase is modulated is shielded by the aperture of an optical system or an aperture by a slit 11 arranged on the focusing surface of the optical system. Then, the optical information obtained by setting the plural times of the minimum interval of the electrode wires as the minimum unit is generated by forming the image of light passed through the aperture.