PURPOSE: To obtain the rapid response of the contraction of an actuator main body, by providing a pair of conductive parts to a gel receiving chamber having a hydrated polymer gel received therein over the almost whole thereof and increasing the contact area of the hydrated polymer gel with the conductive parts.

CONSTITUTION: An actuator main body 1 is constituted by winding a base film 2 in an almost coil shape to form a gel receiving chamber 4 having a hydrated polymer gel 3 received therein and providing a pair of conductive parts 5, 6 to the inner surface of the base film 2. A large number of small holes allowing the gel receiving chamber 4 to communicate with the outside are formed to the coil-shape part 7 of the base film 2 and the diameter of each of the small holes is set so as to prevent the hydrated polymer gel 3 from flowing out to the outside. When water is absorbed by the hydrated polymer gel 3 to bring the actuator main body 1 to a stretched state and predetermined voltage is applied to a pair of the conductive parts 5, 6, the hydrated polymer gel 3 is dehydrated and water is led out to the outside from the gaps d or holes of the base film to contract the actuator main body 1. When the application of voltage to a pair of the conductive parts 5, 6 is stopped, the hydrated polymer gel 3 absorbs water and the actuator main body 1 extends.