PURPOSE: To eliminate the revision of a program, to reduce storage capacity and to prevent burning even when a hour display, etc., exists by lowering display luminance when no luminance change is detected over prescribed frames.

CONSTITUTION: Detection points P are displayed on a display picture 1. The detection points P are preferred to be set so that they are not adjacent each other, and they are uniform for the display picture 1, and they are set in a grid shape. Then, by thinning and setting the detection points P for inspecting whether or not the display picture l is deflected from all pixels on the display picture 1, the storage capacity required for inspection is reduced. In such a manner, by inspecting in the thinning detection points P, the required revision of the picture is detected when the setting of the detection points P is proper. Further, even when the display picture 1 is provided with the hour display 2, since the detection points P are set in discrete, when the detection points P are set avoiding the display part of the hour display 2, the display change of the hour display 2 is avoided from inspection, and the burning is prevented effectively.