A wheel driving system is capable of varying differential limiting torque applied to a differential included in an all-terrain vehicle according to the difference between loads respectively applied to the right and the left wheel of the vehicle, which varies depending on the traveling condition or turning condition of the vehicle. Right and left wheels are connected through a differential gear mechanism (30) having a differential case (46) and held in a reduction gear case (13), an input pinion (22) and a drive shaft to an engine. The differential case (46) and a differential gear shaft (36) connected to the wheel are interlocked by a wet multiple-disk differential limiting mechanism (31) having a friction clutch mechanism immersed in oil. The multiple-disk differential limiting mechanism (31) is operated by a multiple-disk differential limiting mechanism operating mechanism to vary differential limiting torque. The torque transmitting capacity of the differential limiting mechanism (31) is adjusted by operating a turnable operating lever (21) disposed near a handgrip (15) attached to a handlebar included in the all-terrain vehicle.