There is provided a broadly tunable laser beam generator serving as a laser beam source which utilizes a nonlinear optical effect of a silica (glass) fiber and which is broadly tunable in the near-infrared region, having ultra-broad tunability which has not been easily achieved by known tunable lasers, and generating coherent light which can be continuously swept over the entire wavelength region with a simple mechanical operation of a single wavelength selecting element and which is emitted in a constant direction independent of its wavelength.The laser beam source which utilizes a nonlinear optical effect of a silica optical fiber (8) and which is broadly tunable in the near-infrared region has ultra-broad tunability and generates coherent light which can be continuously swept over the entire wavelength region with a single wavelength selecting element (10).