POWER TRANSMITTING DEVICE

To reduce the size of a brake mechanism without impairing the cooling effect of the brake mechanism, a power transmission device includes a spindle case 20 including a brake chamber B and a wheel hub 30 including a final chamber F that communicates with the brake chamber B through a central hole 21a of the spindle case 20. A through hole 22a that causes the brake chamber B to communicate with the final chamber F of the wheel hub 30 is provided in the spindle case 20 and when an axle shaft 1 rotates, oil in the brake chamber B is supplied inside the final chamber F through the through hole 22a by action of centrifugal force due to rotation of a brake mechanism 80.