An actuator of the present invention includes a fibrous polymer material which is rotationally driven about a fiber axis by heating, in which both ends of the fibrous polymer material are fixed by tension stress T (MPa), and a relationship of the following Expression (1) is satisfied between the tension stress T (MPa) and Young’s modulus E (MPa) of the fibrous polymer material in a fiber axial direction.0.011 ´ E £ T £ 0.023 ´ E … (1)本發明之致動器係包括藉由加熱而進行以纖維軸來作為中心之旋轉驅動之纖維狀高分子材料，纖維狀高分子材料之兩端係藉由拉伸應力T（MPa）而進行固定，前述之拉伸應力T（MPa）係在和纖維狀高分子材料之纖維軸方向之楊氏模數E（MPa）之間，具有下列公式（1）之關係。0.011×E≦T≦0.023×E ‧‧‧‧（1）
