PURPOSE: A power train for an automatic transmission is provided to reduce the weight and manufacturing costs by reducing the volume and total length of the auto transmission. CONSTITUTION: In a device, a deceleration planetary gear set outputs rotation of an input shaft(10) to deceleration rotating. A complex planetary gear set outputs change rotation speed of a multi-stage to an output shaft(20). A first actuating element is always restrained by the transmission case(30). A second actuating element is selectively connected to a plurality of actuating elements of the complex planetary gear set. A third actuating element is always connected to an input shaft. A fourth actuating element is always connected to the second actuating element.
