Abstract: In the control device for motor generator in which an engine is started and power generation is performed while a vehicle is running, a field current limit value Ifm in electric driving to start the engine is larger than a field current limit value Ifg in power generation. In the power generation, an inverter mode in a low rotation speed zone for boosting and an alternator mode in a high rotation speed zone for rectifying and outputting a generated voltage without boosting are provided. A field current limit value Ifgi in the inverter-mode power generation and a field current limit value Ifga in the alternator-mode power generation are set differently from each other, and the larger value is set as the value Ifg.