A fiber laser system comprising: a plurality of fiber laser units (2a, 2b, 2c) including respective excitation light sources, said plurality of fiber laser units (2a, 2b, 2c) emitting a plurality of laser beams, said plurality of laser beams passing through a plurality of optical fibers to enter a combiner; the combiner adapted for generating a multi-mode laser beam by combining the plurality of laser beams outputted from the plurality of fiber laser units (2a, 2b, 2c); an output section to which the combined multi-mode laser beam is supplied via a single optical fiber; a plurality of current sources (6a, 6b, 6c) provided so as to correspond to the respective plurality of fiber laser units (2a, 2b, 2c) such that the plurality of current sources supply respective driving currents to corresponding ones of the excitation light sources, wherein the system is configured such that the power (Pw1, Pw2) of each fiber laser unit starts rising at a respective time (t1, t2, t3), after which respective powers of the plurality of laser beams first increase to reach a respective peak (Pe1, Pe2) and subsequently attenuates to be converged onto a steady level (Ps) of a set power; appeal, and a control section for controlling the plurality of current sources (6a, 6b, 6c) so that there is a time interval of a certain time (x) between the adjacent peaks (Pe1, Pe2); wherein the control section is configured to turn on the at least two fiber laser units (2a, 2b, 2c) so that the peaks (Pe1, Pe2) appear in an order decided in advance, wherein the order is an ascending order in terms of a ratio X, which is a ratio of a power of a Stokes beam propagating in a fiber laser unit (2a, 2b, 2c) to a power of a laser beam outputted from the fiber laser unit, such that when the ratio X is small, the reflection resistance of a fiber laser is high; and wherein the control section controls the plurality of current sources so that one of at least two fiber laser units (2a, 2b, 2c), which one has a smallest ratio X among those of the at least two fiber laser units, has a highest output power among those of the at least two fiber laser units. a plurality of fiber laser units (2a, 2b, 2c) including respective excitation light sources, said plurality of fiber laser units (2a, 2b, 2c) emitting a plurality of laser beams, said plurality of laser beams passing through a plurality of optical fibers to enter a combiner; the combiner adapted for generating a multi-mode laser beam by combining the plurality of laser beams outputted from the plurality of fiber laser units (2a, 2b, 2c); an output section to which the combined multi-mode laser beam is supplied via a single optical fiber; a plurality of current sources (6a, 6b, 6c) provided so as to correspond to the respective plurality of fiber laser units (2a, 2b, 2c) such that the plurality of current sources supply respective driving currents to corresponding ones of the excitation light sources, wherein the system is configured such that the power (Pw1, Pw2) of each fiber laser unit starts rising at a respective time (t1, t2, t3), after which respective powers of the plurality of laser beams first increase to reach a respective peak (Pe1, Pe2) and subsequently attenuates to be converged onto a steady level (Ps) of a set power; appeal, and a control section for controlling the plurality of current sources (6a, 6b, 6c) so that there is a time interval of a certain time (x) between the adjacent peaks (Pe1, Pe2); wherein the control section is configured to turn on the at least two fiber laser units (2a, 2b, 2c) so that the peaks (Pe1, Pe2) appear in an order decided in advance, wherein the order is an ascending order in terms of a ratio X, which is a ratio of a power of a Stokes beam propagating in a fiber laser unit (2a, 2b, 2c) to a power of a laser beam outputted from the fiber laser unit, such that when the ratio X is small, the reflection resistance of a fiber laser is high; and wherein the control section controls the plurality of current sources so that one of at least two fiber laser units (2a, 2b, 2c), which one has a smallest ratio X among those of the at least two fiber laser units, has a highest output power among those of the at least two fiber laser units.