A phase difference element, in which imbalance hardly occurs between right and left pictures during displaying a three-dimensional image, and a display device having the phase difference element are provided. A base film of the phase difference element includes, for example, a thin resin film having optical anisotropy. A slow axis of the base film points in a vertical or horizontal direction, and points in a direction intersecting with a slow axis of a right-eye region of the phase difference element and with a slow axis of a left-eye region thereof. Thus, influence due to optical anisotropy of the base film is exerted on each light being transmitted by the base film, so that the influence is not extremely greatly exerted on only one of light corresponding to a right eye and light corresponding to a left eye, the respective light being transmitted by the base film.