In an apparatus, a motor current limit calculator calculates a motor current limit to which a motor current is to be limited. A motor current command calculator calculates a motor current command representing a target value for the motor current. A current command corrector corrects the motor current command as a function of the motor current limit. A motor voltage command calculator calculates a motor voltage command as a function of the corrected motor current command and the motor current, and feed back the motor voltage command to the motor current limit calculator. The motor voltage command represents a target value for a voltage of the output power applied to the motor. The motor current limit calculator calculates the motor current limit in accordance with the motor current, the converter current limit, and the motor voltage command fed back from the motor voltage command calculator.