1. A machine learning apparatus for learning an operating command to an electric motor in a machine tool, the machine learning apparatus comprising a processor configured to: observe an amount of power fed to the electric motor, a temperature of the electric motor, a load of the electric motor, and a vibration of the electric motor as status variables, and perform learning whether or not it is necessary to correct the operating command to the electric motor according to the status variables, and a result of judging whether an abnormality has occurred in the machine tool based on the status variables, wherein, in said learning, the processor is further configured to calculate a reward based on a difference of the amount of power fed and a predetermined amount of power fed, a difference of the temperature and a predetermined temperature, a difference of the load and a predetermined load, and a difference of the vibration and a predetermined vibration, wherein the processor is configured to calculate the reward by increasing the reward when said result of judging indicates that no abnormality has occurred in the machine tool based on the status variables, and decreasing the reward when said result of judging indicates that an abnormality has occurred in the machine tool based on the status variables, and update a function for determining the operating command based on the reward, and wherein the electric motor is controlled by the operating command determined by the updated function.