An image display device includes a display panel which selectively displays a 2D image and a 3D image and includes a plurality of pixels, a patterned retarder for dividing light from the display panel into first polarized light and second polarized light, and a control voltage generation circuit which generates a 2D control voltage at an off-level and generates a 3D control voltage alternately having a slight-on level and the off-level every predetermined period of time. The slight-on level is higher than the off-level and is lower than a full-on level. Each pixel includes a main display unit including a first pixel electrode and a first common electrode and a subsidiary display unit including a second pixel electrode, a second common electrode, and a discharge control switch.