An object of the present invention is to provide a polymer actuator that does not need a special member for determining the output direction of the drive force or a support member, and which is simply configured with a small number of parts and is compact and low-cost. The present invention provides a polymer actuator that includes electrodes which are inelastic in a planar direction and sandwich a stretching portion of a dielectric polymer with a gradient in thickness, and also provides an optical system including the polymer actuator.