An actuator includes a base, a stationary frame mounted on the base, a driving member, a moveable frame, and guide poles. The base includes a plate having an aperture and a ring-shaped protrusion extending from the plate and surrounding the aperture. The driving member includes a piezoelectric motor fixed on the base and a ring-shaped transmission unit having a first end surface and an opposite second end surface. The transmission unit rotatably sleeves on the protrusion. The first end surface contacts the piezoelectric motor. The second end surface defines a wedge-shaped groove. The moveable frame includes a body and a wedge-shaped stripe extending from the body toward the wedge-shaped groove. The moveable frame is supported by the second end surface. The wedge-shaped stripe partially or entirely engages in the wedge-shaped groove. The guide poles extend through the moveable frame.