PURPOSE: To ensure the uniform exposure value to the hologram recording part by shifting the masking shield containing the aperture part or the shielding part at least by the fixed distance to cut off the laser beam.

CONSTITUTION: Masking shield 7' contains aperture part 7", and width W of part 7" is selected to the same value as diameter D of the laser beam. And shield 7' features the reciprocating motion in the same speed via, for example, the voice coil. In other words, the beam is cut off in the state (a), and no irradiation is given to the hologram recording part. Then part 7" shifts sequentially up to the full-open state (c) and then the beam is cut off again at the state (e). And part 7" shifts in the opposite direction, which is repeated, and the shift distance equals to W+D. As a result, the same exposure value is secured at the hologram parts of both beams A and B parts, thus ensuring the uniform amount of exposure at any area excepting parts A and B. The same effect can also be obtained with the light shielding part secured instead of the aperture part and furthermore under the condition of D<W.