An actuator includes a casing, an output disc, a transmission component, a cable, a power source, and a tension adjustment assembly. The output disc and the transmission component are rotatably disposed on the casing. The cable is disposed through the transmission component and connected to the output disc. The power source can drive the transmission component. The tension adjustment assembly includes a lever, an elastic component, and a slidable component. The lever has a first end and a second end opposite to each other. The first end is connected to the cable. The elastic component is connected to the casing and the second end of the lever. The slidable component is in contact with a portion of the lever located between the first end and the second end, and is slidable along the lever to change its position to adjust a tension of the cable.