Piezoelectric polymer film

A piezoelectric polymer film which contains an optically-active helical chiral polymer having a weight average molecular weight of 50,000 to 1,000,000, has a degree of crystallinity of 20 to 80% as determined by a DSC method, has a product of a standardized molecular orientation MORc of the film and the above-mentioned degree of crystallinity of 40 to 700 wherein the reference thickness is 50 μm as measured with a microwave transmission-type molecular orientation meter, and also has an Nz factor falling within the range from 1.108 to 1.140 wherein the Nz factor is expressed by the formula: (Nz factor) = (n x -n z )/(n x -n y ) in which n x represents a refractive index of the film as measured in an in-plane slow axis direction, n y represents a refractive index of the film as measured in an in-plane fast axis direction and n z represents a refractive index of the film as measured in the thickness direction.