A free ball bearing includes a retainer ball-pressing ring, the retainer ball-pressing ring including a substantially cylindrical pressing member inserted in an internal space between the semispherical recessed surface and the main ball toward the base end; the retainer ball-pressing ring being moved from a pressing position to a standby position along the unit center axis by the ring moving mechanism; the pressing member restricting or preventing rotation of the plurality of retainer balls by pressing the plurality of retainer balls when the retainer ball-pressing ring is at the pressing position; and the plurality of retainer balls of which the rotation is restrained or prevented by the pressing member being released when the retainer ball-pressing ring is at the standby position.