the invention relates to a fiber laser apparatus having a structure that enables efficient laser processing for an object and to a laser processing method . the fiber laser apparatus comprises an amplifying section for amplifying seed light by cladding - pumping , and has a structure for further using a residual component of pumping light for cladding - pumping in order to heat the object . in particular , a guiding optical fiber is provided between an amplifying optical fiber of the amplifying section and an output optical system converging the single - mode amplified seed light on the object , the guiding optical fiber serving to increase the degree of freedom in arranging the output optical system . the guiding optical fiber has a structure enabling the single - mode propagation of the amplified seed light outputted from the amplifying optical fiber and multimode propagation of the residual pumping light . because the object is irradiated with the converged amplified seed light , while being heated with the residual pumping light outputted from the output optical system , even an object with a complex shape can be subjected to efficient laser processing .