An all-wheel drive system includes a center differential, a limited-slip differential clutch, a front-wheel torque transmission system, a rear-wheel torque transmission system, and a controller. The center differential distributes torque between front and rear wheels of a vehicle. The limited-slip differential clutch limits a differential operation of the center differential in accordance with an engaging pressure, and changes a front-rear torque distribution ratio between the front and rear wheels. The front-wheel torque transmission system transmits torque between the center differential and the front wheels. The rear-wheel torque transmission system transmits torque between the center differential and the rear wheels. The controller adjusts the engaging pressure based on a driving state of the vehicle. Reduction ratios of the front-wheel and rear-wheel torque transmission systems are set different from each other. The center differential is configured such that the front-rear torque distribution ratio is initially unequal and is changeable.