A plane thin-type polymer actuator is provided with a conductive active member serving as a first electrode layer, and a second electrode layer, with at least a first electrolytic layer made in contact with the active member layer. The first electrolytic layer being sealed between the two electrode layers so that, by applying an electric field between the two electrode layers, the active member layer is expanded and contracted. In this structure, the first electrolytic layer is a solid-state electrolyte having a specific elastic modulus, or a liquid-state electrolyte. A holding member is provided to maintain the thickness between the active member layer and the second electrode layer.