This invention provides a phase difference film characterized in that it comprises a thermoplastic polymer comprising at least a side-chain component (A) aligned in a direction substantially perpendicular to a slow-phase axis direction, the absorption edge wavelength (lambadacut-off) in the side-chain components (A) is not less than 330 nm, and the in-plane retardation value (Re[450]) at a wavelength of 450 nm is smaller than the in-plane retardation value (Re[650]) at a wavelength of 650 nm. In the phase difference film, the difference between the in-plane retardation value (Re[650]) at a wavelength of 650 nm and the in-plane retardation value (Re[450]) at a wavelength of 450 nm, i.e., deltaRe650-450 = Re[650] - Re[450], is preferably not less than 10 nm. The phase difference film has such optical properties that the birefringence index within the plane is large and the difference between the retardation value on the short wavelength side and that on the long wavelength side is large.