A phase difference plate which comprises one sheet of polymer film containing a compound having a rod-shaped molecular structure and exhibiting a maximum absorption wavelength (.lamda.max) of less than 250 nm in an ultraviolet spectrum of its solution and which exhibits a retardation value as measured at a wavelength of 450 nm (Re450) of 60 to 135 nm and a retardation value as measured at a wavelength of 590 nm (Re590) of 100 to 170 nm, where the relationship: Re590-Re450.gtoreq.2 nm is satisfied. The phase difference plate functions as a .lamda./4 plate.