PURPOSE: To shorten the oscillating time of one code, and to equalize the thermal effect of each code by generating trigger signals at time intervals corresponding to values represented by the parallel bits of parallel pulse signals and generating laser beams synchronizing with the trigger signals.

CONSTITUTION: Binary code signals 6 generated in a binary code signal generating circuit 1 are multiplied by specific pulse row signals in a scrambling circuit 2, and scrambled code signals in which the rate of 0 and 1 constituting codes is approximately the same are generated. A series-parallel converting circuit 3 converts the code signals into two parallel pulse codes. A trigger signal generating circuit 4 transmits trigger signals 9 at time intervals corresponding to the parallel pulse codes over an oscillator 5. The laser oscillator 5 generates laser beams at a point of time when it is driven by the laser oscillating trigger signals 9.