A fiber laser device (FL) comprising: an amplifying fiber (AF) comprising a first end and a second end; a delivery fiber (DF) having an input end and an output end and being configured such that laser light that is output from the second end of the amplifying fiber (AF) is guided in the delivery fiber (DF), the second end of the amplifying fiber (AF) being connected to the input end of the delivery fiber (DF); and a Raman filter (RF) provided at a selected position in the delivery fiber (DF), which Raman filter (RF) is configured to reflect a part of Raman scattered light power that is generated by stimulated Raman scattering caused to the laser light, and to transmit a part of said Raman scattered light power that is generated by stimulated Raman scattering caused to the laser light; the Raman filter (RF) being provided so that the following inequality (a) is satisfied: where: L1 represents a length of a first light path from the first end of the amplifying fiber (AF) to the Raman filter (RF); g1 represents gain which the Raman scattered light receives per unit length in the first light path; L2 represents a length of a second light path from the Raman filter (RF) to the output end of the delivery fiber (DF); g2 represents gain which the Raman scattered light receives per unit length in the second light path; am represents a reflection attenuation by the Raman filter (RF) of said Raman scattered light power; at represents a transmission attenuation by the Raman filter (RF) of said Raman scattered light power; and ar represents a reflection attenuation of said Raman scattered light power by a workpiece (W) which is processable by the laser light output from the fiber laser device. an amplifying fiber (AF) comprising a first end and a second end; a delivery fiber (DF) having an input end and an output end and being configured such that laser light that is output from the second end of the amplifying fiber (AF) is guided in the delivery fiber (DF), the second end of the amplifying fiber (AF) being connected to the input end of the delivery fiber (DF); and a Raman filter (RF) provided at a selected position in the delivery fiber (DF), which Raman filter (RF) is configured to reflect a part of Raman scattered light power that is generated by stimulated Raman scattering caused to the laser light, and to transmit a part of said Raman scattered light power that is generated by stimulated Raman scattering caused to the laser light; the Raman filter (RF) being provided so that the following inequality (a) is satisfied: where: L1 represents a length of a first light path from the first end of the amplifying fiber (AF) to the Raman filter (RF); g1 represents gain which the Raman scattered light receives per unit length in the first light path; L2 represents a length of a second light path from the Raman filter (RF) to the output end of the delivery fiber (DF); g2 represents gain which the Raman scattered light receives per unit length in the second light path; am represents a reflection attenuation by the Raman filter (RF) of said Raman scattered light power; at represents a transmission attenuation by the Raman filter (RF) of said Raman scattered light power; and ar represents a reflection attenuation of said Raman scattered light power by a workpiece (W) which is processable by the laser light output from the fiber laser device. <EOS>