A retardation plate having a high film strength and having an optical property is provided by using a biaxial liquid crystal compound, in which the direction having a minimum refractive index of the optically anisotropic thin layer almost coincides with the normal direction in the film plane of the retardation plate, and the retardation plate comprises a transparent support and at least one optically anisotropic layer containing a liquid crystal compound capable of expressing a biaxial liquid crystal phase, wherein the liquid crystal compound is a polymerizable compound and/or a polymer compound.