The present invention relates to an image processing apparatus, which calculates the histogram of an image on the basis of moving image information that is input in real time, and corrects and outputs the brightness of the image using the histogram in real time. The apparatus for controlling the brightness of moving image signals according to the present invention includes a cumulative difference function detection means, an image storage means and a brightness adjustment means. The cumulative difference function detection means calculates a cumulative difference function using upper n bits of each input image. The image storage means stores therein the input image. The brightness adjustment means adjusts the brightness of the image in real time using the cumulative difference function calculated by the cumulative difference function detection means when the input image stored in the image storage means is displayed.