Inverter circuits are provided for motor winding sets, respectively. Control units are provided for the motor winding sets to generate control signals related to driving of the inverter circuits and control currents flowing through the motor winding sets, respectively, thereby controlling driving of a motor. The control mode includes a manual steering mode for controlling the motor according to a steering operation on a steering wheel by a driver and an automatic steering mode for controlling the motor independently of the steering operation on the steering wheel by the driver. The control units are capable of switching the control modes and differentiate the current control according to the control mode. By making the current control different according to the control mode, it is possible to attain optimal characteristics which correspond to each control mode.