An actuator includes: a first motor including a first stator and a first rotor; a second motor and including a second stator and a second rotor; a shaft member penetrating through the first rotor and the second rotor, and including a first part protruding from the first rotor toward an opposite side to the second rotor and including a spline groove, and a second part protruding from the second rotor toward an opposite side to the first rotor and including a male screw portion; a spline outer cylinder engaging with the spline groove to guide the shaft member and configured to rotate together with the first rotor to enable the shaft member to rotate; and a nut member provided with a female screw portion engaging with the male screw portion of the shaft member, and configured to rotate together with the second rotor to enable the shaft member to move.