A machine learning apparatus includes a state observation unit which observes a state variable including at least one of data associated with the value of a DC voltage in a DC link, data associated with the amount of power supply regeneration representing the amount of power returned from the DC link to an AC power supply by a power supply regeneration operation by a converter, and data associated with the occurrence or nonoccurrence of an overvoltage alarm indicating that the DC voltage of the DC link has exceeded a preset overvoltage alarm level, and a learning unit learns conditions associated with the power supply regeneration operation by the converter, in accordance with a training data set defined by the state variable.