An optical information recording/reproducing apparatus, to apply holograms of an angle multiplex recording method therein includes: a light source to emit a light beam; a divider unit to divide the light beam into a signal beam and a reference light; an angle variable unit to change an angle of the reference light incident upon an optical information recording medium; a spatial light modulator unit to add information to the signal beam; an objective lens to irradiate the signal beam on the medium; an image pickup unit to detect a diffracted light generating from a recording region, when the reference light is irradiated on the medium; and an optical element to shape a form of light flux of the reference light, so that a light flux diameter of the reference light in a multiplex direction becomes larger than the light flux diameter of the reference light in a pitch direction.