A conductive polymer doped with a dopant can be expanded and contracted when electrically oxidized and reduced in a driving electrolytic solution containing an anion, and thereby can act as an actuator element in an actuator. The anion is a fluorine-containing ion derived from a strong acid, and the dopant is an aromatic sulfonate ion free of fluorine. The conductive polymer is a polymer containing a 5-membered heterocyclic moiety as a repeating unit, such as a polypyrrole or a polythiophene. When the conductive polymer is in an oxidized state, at least part of the 5-membered heterocyclic moieties has a carbonyl group.