To provide an actuator capable of materializing change over of manual and automatic operations and the speed change of an output shaft with a simple structure, a valve device and a damper device using the same.

A manual/speed change clutch gear 8 comprising a plurality of gears concentrically and integrally rotating is moved and operated along a fixed shaft 9. Consequently, engagement of a transmission gear in a front stage side or a transmission gear in a rear stage side, and the manual/speed change clutch gear 8 is released, and gears giving desired gear ratio between the transmission gear in the rear stage side and the manual/speed change clutch gear 8 are meshed.