To enhance added value by providing a brake assisting function applying rotational resistance to wheels when braking torque is larger than driving torque in a bearing device for an axle.

In the bearing device for the axle, a mechanical clutch 4 is incorporated between a hub wheel 1 and a cylinder 34, power is smoothly transmitted when a relationship between the driving torque T1 and the braking torque T2 is T1>T2, and braking is assisted by cutting off power transmission and applying rotational torque to the hub wheel 1 when T1≤T2. Since the brake assisting function is provided in addition to original functions of a bearing device for the axle, it can contribute to improvement of fuel consumption performance or braking performance in a vehicle such as supporting braking force by an engine brake or a disc brake device in the vehicle.