Abstract text

An optical information recording and reproducing apparatus for recording information on a recording medium by forming interference fringes generated by interference between an information beam and a reference beam on the recording medium and for reproducing the information by irradiating, with the reference beam, the recording medium, in which the interference fringes are formed. The apparatus includes a spatial light modulator for spatially modulating at least a portion of a light beam emitted from a light source into the information beam. A light sensing device reads the information beam extracted from the recording medium by the reference beam irradiated on the recording medium. A shift amount detector detects a shift of the irradiating position of the light beam entering the spatial light modulator, and a device corrects a positional shift between a position of an area for modulating the information beam and a position of the light beam in the spatial light modulator based on a positional shift amount detected by the shift amount detector.