Provided herein is a retardation optical element 10 that produces no bright and dark fringes on a displayed image even when placed between a liquid crystal cell 104 and a polarizer 102B and thus can effectively prevent lowering of display quality. The retardation optical element 10 includes a retardation layer 12 having a cholesteric-regular molecular structure with liquid crystalline molecules in planar orientation. The helical pitch in the molecular structure of the retardation layer 12 is so adjusted that the retardation layer 12 can, owing to its molecular structure, selectively reflect light whose wavelength falls in a range different from the wave range of light incident on the retardation layer 12 (the selective reflection wave range of the retardation layer is either shorter or longer than the wave range of the incident light). Further, the retardation layer 12 has two opposite main surfaces (larger surfaces) 12A and 12B that are perpendicular to each other in the direction of thickness, where the directions of the directors Da of the liquid crystalline molecules on the entire area of the one surface 12A are substantially the same, and those of the directors Db of the liquid crystalline molecules on the entire area of the other surface 12B are also substantially the same.