<p>This laser device is provided with: an optical-fiber laser for outputting a laser beam; and a process optical fiber serving as a multimode optical fiber that has a larger core diameter and a numerical aperture equal to or larger than the optical fiber positioned in the output-side last stage of the optical-fiber laser, and which is used to propagate and output the laser beam output by the optical-fiber laser. Preferably, the optical-fiber laser outputs a fundamental-mode laser beam, and the optical fiber positioned in the output-side last stage of the optical-fiber laser has a length equal to or smaller than a boundary value at which the ratio between the total power value of a Raman-scattered light at the optical output end of the process optical fiber and the total power value of the laser beam increases drastically.</p>
