The present invention greatly reduces the likelihood that fiber fusion will occur. A laser apparatus comprises an excitation light source and an optical amplifier unit, which optically amplifies by receiving excitation light that is output from the excitation light source and that transits an optical fiber. A monitor unit monitors the power level of the excitation light transmitted from the excitation light source to the optical amplifier unit side via the optical fiber. At the initial start of the output of the excitation light from the excitation light source, once the excitation light is being output at the prescribed power level by the excitation light source, the control unit performs control such that the excitation light at a power level higher than the prescribed power level is output if the power level monitored by the monitor unit is greater than or equal to a prescribed value when the excitation light at the prescribed power level is being output from the excitation light source and such that the output of the excitation light is stopped if the power level monitored by the monitor unit is less than the prescribed value when the excitation light at the prescribed power level is being output from the excitation light source.
