To reduce power consumption of an image display device by decreasing a light quantity of backlight without losing brightness of an image of the image display device in appearance.

An image signal in an RGB format which is inputted from a control part 1, and an image signal which is emphasized on a brightness signal component through a conversion from the image signal in RGB format into that in YCbCr format in a converter part 2, an emphasis on the brightness component Y in a brightness emphasis part, and an inverse conversion into the RGB format in the inverse conversion part 4 are inputted to a multiplexer 5. When the control part 1 is set to an electric power saving mode for reducing the light quantity of backlight lower than normal, it controls a backlight power source 10 to reduce the light quantity of the backlight module; selects at the same time an image signal emphasized on the brightness signal component in a multiplexer 5 to write the signal to frame memory 6; and displays it on an LCD module 7 through reading.