To solve a problem in which a fiber laser that has been conventionally proposed as a white light source which is an important device for measuring the wavelength-dependent characteristics of an optical fiber and an optical component does not have sufficient characteristics for a high-precision measuring instrument in terms of high stability and high brightness.SOLUTION: An optical fiber output light source device includes an optical path in which an amplification optical fiber and a dispersion compensation optical fiber are connected via a polarization controller and a combiner, a 90° polarization rotation reflector connected to one end of the optical path, a single polarization reflection type polarization beam splitter connected to the other end of the optical path, a reflector arranged to face a reflected light plane of the single polarization reflection type polarization beam splitter, and an excitation light source connected to the combiner, and has unprecedented intensity stability and wavelength control performance, and can demonstrate sufficient performance as a white light source.SELECTED DRAWING: Figure 1