Abstract: The present invention provides an actuator, comprising a fiber and a temperature regulator capable of at least one of heating and cooling the fiber. The fiber is twisted around a longitudinal axis thereof. The fiber is folded so as to have a shape of a cylindrical coil. The fiber is formed of linear low-density polyethylene. The following mathematical formula (I) is satisfied: D/d<1 (I), where D represents a mean diameter of the cylindrical coil; and d represents a diameter of the fiber.