A required-generate-current (RGC) is calculated according to conditions of the electric loads and a charging state of the battery. The required-alternator-drive-torque (RADT) is estimated according to the required-generate-current (RGC). A required engine torque is calculated by adding the required-alternator-drive-torque (RADT) and the required-vehicle-drive-torque (RVDT) together. The engine torque which is realized at next calculating timing is estimated in consideration of a response delay of the engine. The differential torque between the estimated engine torque and the required-vehicle-drive-torque (RVDT) is calculated as the permission torque. The command current corresponding to the permission torque is calculated. The control current of the alternator is controlled in such a manner as to generate current corresponding to the command current at the next calculating timing.