Provided are an image brightness control device and an image brightness control method for improving the definition of brightness of the entire image and/or improving the definition of brightness of local areas using local brightness information. The image brightness controlling device includes: a preprocessing unit acquiring an offset table for controlling a dynamic range corresponding to an image range of an input image using brightness values of color data of the input image; and a tone mapping unit mapping the offset table onto the color data. It is possible to improve the definition of brightness so as to correspond to the characteristic of the input image, by automatically considering how to reflect a distribution characteristic of an image.