An image display device is provided which is capable of improving reproducibility of a white color. An RGB video signal is converted by a gamma converting section into three color luminance values and the maximum luminance value and minimum luminance value of the three color luminance values are calculated by a Min/Max calculating section. The first four color luminance values are calculated by an RGB luminance calculating section. A scaling factor is calculated by a scaling factor calculating section based on the first four color luminance values and the maximum luminance value. The second four color luminance values are calculated by an RGBW scaling luminance calculating section based on the first four color luminance values and on the scaling factor. An RGBW video signal corresponding to a gray level value of four color is generated by a reverse gamma converting section.