A flat display device includes a display panel. The display panel includes a unit pixel, the unit pixel having a red sub-pixel, a green sub-pixel, a blue sub-pixel, and a white sub-pixel. The flat display device further includes a panel driving unit to drive the flat panel in a first driving period and a second driving period in an alternating manner to display a white image on the unit pixel. The panel driving unit generates first white unit data, to enable two of the red, green, and blue sub-pixels and the white sub-pixel to be driven in the first driving period. The panel driving unit generates second white unit data, to enable three of the sub-pixels, which include the sub-pixel not driven in the first driving period, to be driven in the second driving period.