A machine learning device observes a state variable of the inside and the outside of a laser device including time-series data of light output, which is detected by an output light sensor, and a light output command through a control unit of the laser device, and acquires a determination result on correctness with respect to a quantitative failure occurrence mechanism outputted for each failure in the laser device. The machine learning device learns the quantitative failure occurrence mechanism corresponding to each failure while associating the quantitative failure occurrence mechanism with the state variable and the determination result on correctness with respect to the quantitative failure occurrence mechanism, and decides a quantitative failure occurrence mechanism which is to be outputted when an occurrence of each failure is detected.