PURPOSE: To perform laser beam position control and the generation of an irregular spot array in real time by composing the optical device of a liquid crystal light valve, lens groups which are arranged in front of and behind it, and a pattern generator for recording a computer hologram in this liquid crystal light valve.

CONSTITUTION: The laser beam 109 projected by a laser light source 103 becomes expanded parallel light through a collimator lens 105 and is made incident on the liquid crystal light valve 106, and a liquid level is modulated through the operation of the computer hologram recorded in the valve 106 to form a spot or spot array 110 on an output surface 108. A PC 101 generates a video signal at the time of recording the computer hologram in the valve 106 and the signal is inputted to the light crystal light valve through an interface circuit 103. When the computer hologram which is recorded in the valve 106 is rewritten at a high speed, pattern data stored in a video memory 102 previously are read out one after another and the laser beam spot changes in position or array almost in real time.