the cumulative light emission time t u is longer than the cumulative light emission time t l and the difference between them is larger than the threshold value t tl step s 202 n step s 203 y a lower side display instruction is provided step s 207 the lower driver 19 b of the bl driver 19 which receives the lower side display instruction turns the lower backlight 20 b on to illuminate a lower side sub region of the liquid crystal cell array 17 step s 208 and the upper driver 19 a turns the upper backlight 20 a off at the same time the scaler 15 performs scaling lower side scaling which downsizes an image so as to match the lower side sub region and fits the video signal into the lower side sub region of the liquid crystal cell array 17 step s 209 thereby as shown in fig3 c an image is displayed on the lower side sub region of the liquid crystal panel in this case the upper backlight 20 a is turned off so the power consumption may be saved when the difference between the cumulative light emission time t u and the cumulative light emission time t l does not exceed the threshold value t tl step s 202 n step s 203 n display switching between the upper side sub region and the lower side sub region is not performed thus in the liquid crystal.