A driving force control system for a four-wheel drive vehicle. An automatic-mode transmitted torque is calculated based on operating conditions of the vehicle. When lock mode-executing conditions including operation of a lock switch by the driver are satisfied, a lock mode in which the engagement forces of the clutches are set to a lock-mode transmitted torque, including a lockable transmitted torque which can lock the front wheels and the rear wheels to each other. Further, the lock mode transmitted torque is limited depending on a traveling condition of the vehicle such that the lock-mode transmitted torque is held below the lockable transmitted torque. When the automatic-mode transmitted torque is larger than the limited lock-mode transmitted torque during the lock-mode, the engagement forces of the clutches are set to the automatic-mode transmitted torques.