To provide a fluorescence observation endoscope system capable of equalizing the light intensity of exciting light emitted from each of a pair of light distribution lenses.

A light guide 16 comprises two light fiber bundles 16a, 16b each of which keeps the proximal end and the tip end mutually separated. The exciting light emitted from a laser diode group 34 of each set among two sets of the laser diode group 34 to which driving current is supplied respectively from respective LD output control circuits 32, 33 is synthesized through relay fibers 35, 36, and enters the proximal end face of corresponding light fiber bundle 16a through an original light path. A system control circuit 44 calculates the luminosity value of an image signal obtained by an image element 14 imaging a fluorescence image. Luminosity values obtained on both LD control circuits 32, 33 are made mutually in agreement by adjusting the electric current value which respective LD control circuits 32, 33 supply to respective laser diodes.