A laser light irradiation system that irradiates a stone in a body with laser light to cause the stone to be dust, the laser light irradiation system including a laser fiber that emits the laser light, and a processor configured to control a frequency of the laser light emitted from the laser fiber, wherein the processor is configured to switch between first laser light of a first frequency and second laser light of a second frequency such that the second laser light is emitted at least before or after an emission timing of the first laser light, the first laser light generating a water flow that pulls the stone toward the laser fiber, the second laser light generating a water flow that stirs the stone.