Power distribution control apparatus for four-wheel drive vehicle

A four-wheel drive vehicle includes a caupling, which varies the distribution ratio of torque to the front wheels and the rear wheels. The distribution ratio of torque to the front wheels and the rear wheels is determined by the engaging force of the coupling. An ECU sets first to third determination threshold values for the opening degree of a throttle valve of an engine in accordance with the detected vehicle speed. The ECU determines whether the vehicle is in a steady driving state by comparing the detected throttle opening degree with the set first to third determination threshold values and controls the engaging force of the coupling in accordance with the determination result. Thus, the steady driving state of the vehicle is correctly determined.