An image processing unit (2 in FIG. 1) discards a high gray level side of input image data (RiGiBi) in accordance with a chroma coefficient (Csc), thereby to generate a signal of lowered chroma, and it expands the signal into output image data (RoGoBo) of full scale. Besides, the image processing unit (2) generates an image adjustment parameter (Th) and performs a control so as to reduce power of backlight (6), in interlocking with the full-scale expansion.