A circulation-accelerating light irradiation system capable of irradiating a focus part with light with such a wavelength as to show a high vasodilating action is provided. When a therapy start signal is inputted by the user or the like, a control unit 13 starts controlling a laser beam generation unit 12. The laser beam generation unit 12 generates laser beams 15 according to the control of the control unit 13. The laser beams 15 thus generated are transmitted through optical fibers 10, and are converted into parallel beams by collimator lenses 11. The laser beams 15 converted into the parallel beams are radiated onto a living body, and are concentrated onto a target part 51. The diseased part is treated with the energy of the concentrated laser beams 15. This makes it possible to set the output energy of each individual laser beam 15 to a low level, to reduce the influence of the laser beams 15 on the skin surface on which the laser beams are directly incident, and, on the other hand, to apply a sufficient optical energy to the diseased part 51.
