A stereoscopic image display device including at least an image display panel and a patterned phase difference plate disposed on an image-displaying side of the panel, the patterned phase difference plate includes at least a supporter and a patterned optical anisotropic layer having, on the supporter, first phase difference regions and second phase difference regions which are different in either or both an in-plane slow axis direction and a phase difference, and are alternately disposed in a stripe shape, and, in the supporter, a linearity, which is a meandering width in a direction perpendicular to a direction along the pattern of the patterned optical anisotropic layer, of an edge in a direction along a pattern of the patterned optical anisotropic layer is 0.0195% or less of a length in the direction perpendicular to the direction along the pattern of the patterned optical anisotropic layer in the image display panel.