Provided is a wheel driving device which drives a wheel by output rotation of a reduction device disposed on an inside in a radial direction of the wheel. The reduction device includes an output member connected to the wheel, and a pair of bearings supporting the output member. In the pair of bearings, the bearing on a side opposite to a vehicle body has a smaller outer diameter than that of the bearing on a vehicle body side. An injection passage member of a medium injected into the wheel may be disposed on an outside in a diameter direction of the bearing on the side opposite to the vehicle body.