A 2-dimensional (2D)/3-dimensional (3D) image display device generates 2D or 3D image data according to an input image signal and displays them on a display unit. The display unit includes a display panel for displaying an image in response to the 2D or 3D image data and an optical element layer operative during first and second driving modes in accordance with the 3D and 2D image data. A controller converts the optical element layer to be in the first driving mode in a first period before a 3D image signal is displayed when the input image signal changes from a 2D image signal to the 3D image signal, and converts the optical element layer to be in the second driving mode in a second period after the 2D image signal is displayed when the input image signal changes from the 3D image signal to the 2D image signal.