A laser oscillator that, in accordance with a laser output instruction value or a current instruction value that is input, excites a laser medium and obtains a desired laser output comprises: reference waveform generation unit for employing the laser output instruction value or the current instruction value to generate a laser output waveform and a current waveform, which are references; a first comparison unit for obtaining, as a current monitor value, a current value used to excite the laser medium, and for comparing the current value with the current wave form generated by the reference wave form generation unit; and a second comparison unit for fetching, as a laser output monitor value, the value of a laser that is output by exciting the laser medium, and for comparing the value for the laser with the laser output waveform generated by the reference waveform generation unit, wherein an abnormality is detected.