An electronic control apparatus includes target FR calculator that calculates a target exciting current duty ratio FR based on an exciting current inputted from FR terminal of a regulator and flowing through field coil, and information of engine operating conditions. The electronic control apparatus also includes target FR limit value FRCLP calculator that calculates a FRCLP corresponding to a drive torque limit value based on an output of a correlative information detector. A comparator compares target FR and FRCLP, outputs a control signal within FRCLP to a control unit, and controls a duty ratio FR of exciting current flowing through a field coil not to be larger than FRCLP.