To provide an actuator which can adjust a lumber support selectively in front/back and top/bottom positions by a single actuator.

The actuator is provided with a worm gear and a worm wheel which decelerate the output of an electric motor 2, a disc-like plate which is supported in a rotatable manner by the same shaft as the worm wheel, a sun gear 11 which is connected directly to the same shaft as the worm wheel, a planet gear 13 which is engaged with the sun gear 11, and an internal gear 15 which forms an internal teeth that are engaged with the planet gear 13. Two cables 5 are fixed on the internal gear 15 and the disc-like plate, respectively, and when either one of the internal gear 15 and the disc-like plate is rotated the corresponding cable 5 is actuated.