This invention relates to an electrochemical device which comprises a molding containing as a main ingredient a copolymer (Z) and at least two mutually insulated electrodes in joint with the molding, wherein the copolymer (Z) comprises a polymer block (A) having as a main unit an aromatic vinyl compound unit and a polymer block (B) being incompatible with the polymer block (A), and has ion-conducting groups on the polymer block (A). The electrochemical device of the invention can be used particularly as an actuator device.