According to an embodiment of the invention, even if a sample-and-hold circuit samples a signal from a signal processor to a display unit, an image quality reduction is hard to occur. According to an embodiment of the invention, there is provided a flat-panel display device includes a phase control circuit setting a state that a first parallel arrangement RGB pixel signal shifts by 120 degrees, a sample-and-hold circuit sampling a second parallel arrangement RGB pixel signal parallel-output from the phase control circuit to obtain a series arrangement RGB pixel signal, which is three times as much as a single pixel signal, and a driver supplying the series arrangement RGB pixel signal to the corresponding display pixel.