An inner-ring restraint device of a hub bearing capable of restraining an inner ring efficiently without applying a load to the hub bearing. An inner-ring restraint device includes a restraint ring allowing a plurality of pieces to be arranged to form a ring shape and restricting an inner ring of a hub bearing by reducing a diameter, a support plate having a ring shape coaxial with the hub bearing, being provided so as to move in an axial direction and supporting the restraint ring at a position closer to the hub bearing for the vehicle than the restraint ring in the axial direction and a ring-shaped operation plate connected to the support plate so as to relatively move in the axial direction and applying a pressure in a direction of reducing the diameter to the restraint ring by coming relatively close to the support plate.