PURPOSE: To effectively display plural windows by providing a brightness control means for making the brightness of a window which is specified different from the brightness of a window which is not specified.

CONSTITUTION: By inputting display data formed by a mouse 3 and a keyboard 4 in a computer 2, only the window specified by the mouse 3, etc., is displayed on a display 1 as it is, and the window other than the specified one is displayed on the display 1 after lowering the brightness. Therefore, the brightness of the window which is noticed in the case of displaying plural windows is made relatively high and the display of the window is made clear, and the other window is displayed to be inconspicuous by making the brightness of the other window relatively low. Thus, visual field is prevented from being narrowed because of the overlap of the windows and the limitation of a window area and many pieces of information are displayed so as to be easily understood.