Abstract: An actuator includes a motor including a first rotor rotatable in a circumferential direction, and a stator to drive the first rotor; a second rotor rotatable in the circumferential direction; and a speed reducer that reduces rotation of the first rotor and transmits a torque to the second rotor via a bearing. The first and second rotors include first and second tube portions extending in an axial direction, respectively. The second tube portion is radially outward of the first tube portion. A lubricant is filled in a filling space including at least a portion of a space between an outer surface of the first tube portion and an inner surface of the second tube portion. The actuator includes a width reducing portion that reduces a width of the filling space in a radial direction in at least a portion of the filling space in the axial direction.