The backlight apparatus allows brightness control with minimum image quality deterioration. This apparatus has: an illuminating section that radiates illumination light on a back of a liquid crystal panel comprising a plurality of image display areas; and a brightness determining section that determines a light emission brightness value of the illuminating section and renews a light emitting state of the illuminating section, based on the determined light emission brightness value. The illuminating section has light emitting areas illuminating each of a plurality of image display areas. The brightness determining section determines light emission brightness values of the image display areas, from values acquired by applying weights to the information based on input image signals of the image display areas, and changes the weights for the information based on luminance of ambient light surrounding the backlight apparatus.