R, G, B laser beams emitted from an R_LD, a G_LD, and a B_LD, respectively, are divided, through demultiplexers, into respective monitoring laser beams and respective irradiation laser beams to be applied to a scanning type endoscope side. R, G, B drive currents for causing light emission at the R_LD, the G_LD, and the B_LD are controlled such that the light quantities of the divided monitoring laser beams become equal to monitoring light quantity values on which the division ratios in the case of temperature change are reflected. As a result of this control, the light quantities of the irradiation laser beams each fall within a range satisfying a predetermined condition.
