PURPOSE: To execute a spectrum without changing the peak output of a laser light and to perform plural laser beam machinings by distributing a pulse light on each pulse unit by the reflection plate driven by synchronizing with the pulse period of the pulse light outputted from a laser oscillator.

CONSTITUTION: The pulse light of the laser light outputted from a laser oscillator 1 is subjected to a spectrum by a spectral device 20 and the light of one part is reflected dy a total reflection mirror 3a and condensed by a condensing lens 4a. The light of the other part is reflected by a total reflection mirror 3b and condensed by a condensing lens 46. At this time, the reflection plate 21 of the spectral device 20 is driven by a motor 22 and the motor 22 is controlled at its rotation by a control device 23 so as to rotate by synchronizing with the pulse light, so the pulse light is reflected in (e), (f) directions respectively. Therefore the pulse light is acted so as to distribute by reflection faces (g), (h) on each pulse unit and the distributed pulse light is condensed by the condensing lenses 4a, 4b respectively.