The present invention provides an actuator large in the amounts of displacement and generative force. The actuator includes a pair of electrode layers and an electrolyte-containing electrolyte layer interposed between the pair of electrode layers, and transforms upon application of a voltage thereto to cause ions in the electrolyte to migrate, wherein the electrolyte layer includes at least one polymer fiber layer made of polymer fibers and at least some of the polymer fibers of the polymer fiber layer are uniaxially oriented within a plane of the electrolyte layer.