PURPOSE: To enable the output fluctuations of a laser oscillator be readily suppressed by detecting the reflected light from the hologram of laser light during accessing of character pattern groups, reading the output fluctuations of the light source and determining amplification degree by the value thus obtained.

CONSTITUTION: A light intensity detector 48 is disposed in the position where the reflected light 43 of a laser 41 for reconstruction arrives at the time of accessing a desired hologram from a hologram information plate 46 and radiating said laser to the hologram 47. An automatic gain control unit which is so constituted as to increase the amplification degree of a video amplifier 49 when the light intensity is weak at the time by using e.g. field effect transistors and the like is provided so that the image output of always a fixed level may be obtained without changing the quantity of light. As a result of this, the occurrence of any difference in reflectance depending upon holograms is obviated and the light source fluctuation correction in the pattern generator may be performed.