A brightness adjusting apparatus of a reflective type liquid crystal display device is applicable to a portable game machine, for example. The portable game machine is provided with a reflective type color liquid crystal display device, and displayed colors of a game character and a background are determined on the basis of color data included in color palettes. When a player inputs an instruction for brightness adjustment, a brightness adjusting screen is displayed in response thereto, and the color data included in each of an OBJ color palette and a BG color palette is converted on the basis of an adjustment value (parameter) corresponding to designated brightness, and then, the brightness of the object and the brightness of the background are individually adjusted.