In a polymer actuator provided with a first polymer structural member having a conductive property, an electrolyte retention layer electrically connected to the first polymer structural member, and a second polymer structural member electrically connected to the first polymer structural member through the electrolyte retention layer interposed therebetween and having a conductive property, and by applying a potential difference between the first polymer structural member and the second polymer structural member, the first polymer structural member and the second polymer structural member are allowed to expand and contract, by displacement of the second polymer structural member, the potential difference between the first polymer structural member and the second polymer structural member is changed.