[Object] An object of the invention is to provide a fiber laser device capable of stabilizing intensity of laser light output therefrom.[Means to attain the object] A fiber laser device 100 includes: an pumping light source 11 configured to output pumping light; a rare earth-doped fiber 20 to which the pumping light is input; and a first FBG 30 formed on one side of the rare earth-doped fiber 20 and a second FBG 40 formed on the other side of the rare earth-doped fiber 20 that are configured to reflect light amplified in the rare earth-doped fiber 20, wherein the second FBG 40 has a reflectance lower than that of the first FBG 30, a reflection wavelength band in that of the first FBG 30, and Bragg wavelength on short wavelength side of Bragg wavelength of the first FBG 30.