A display controller comprising: an LCD including a liquid crystal panel with a surface configured to display an image and a backlight operable to illuminate the entire surface of the liquid crystal panel from below the liquid crystal panel; a touch panel laminated above the LCD; a display control section operable to display an operation screen on the surface of the liquid crystal panel at a predetermined reference brightness by adjusting an electric signal to be supplied to the backlight, the operation screen having a plurality of instruction images (T1, T2, T3) arranged thereon and each depressable to input a specific operator instruction; a depression detection section operable to detect a depression of each of the instruction images (T1, T2, T3); a brightness adjustment section operable, when a depression of one of the instruction images (T1, T2, T3) is detected by the depression detection section, to instruct the display control section to change brightness of the operation screen from the reference brightness by a change amount preliminarily associated with said depressed one of the instruction images; a cumulative number-of-times value storage section configured to store therein a cumulative number-of-times value with which a depression of each of the instruction images (T1, T2, T3) is detected by the depression detection section; a cumulative number-of-times value updating section operable, when a depression of one of the instruction images (T1, T2, T3) is detected by the depression detection section, to update the cumulative number-of-times value of said depressed one of the instruction images stored in the cumulative number-of-times value storage section; and a change amount updating section operable to set the change amount associated with a first one of the instruction images (T1, T2, T3) whose cumulative number-of-times value stored in the cumulative number-of-times value storage section is a first cumulative number-of-times value, in such a manner as to become greater than the change amount associated with a second one of the instruction images (T1, T2, T3) whose cumulative number-of-times value stored in the cumulative number-of-times value storage section is a second cumulative number-of-times value smaller than the first cumulative number-of-times value; wherein the change amount updating section is configured to update the change amount associated with each one of the instruction images in such a manner as to become smaller as the cumulative number-of-times value of the depression detected by the depression detection section becomes smaller. an LCD including a liquid crystal panel with a surface configured to display an image and a backlight operable to illuminate the entire surface of the liquid crystal panel from below the liquid crystal panel; a touch panel laminated above the LCD; a display control section operable to display an operation screen on the surface of the liquid crystal panel at a predetermined reference brightness by adjusting an electric signal to be supplied to the backlight, the operation screen having a plurality of instruction images (T1, T2, T3) arranged thereon and each depressable to input a specific operator instruction; a depression detection section operable to detect a depression of each of the instruction images (T1, T2, T3); a brightness adjustment section operable, when a depression of one of the instruction images (T1, T2, T3) is detected by the depression detection section, to instruct the display control section to change brightness of the operation screen from the reference brightness by a change amount preliminarily associated with said depressed one of the instruction images; a cumulative number-of-times value storage section configured to store therein a cumulative number-of-times value with which a depression of each of the instruction images (T1, T2, T3) is detected by the depression detection section; a cumulative number-of-times value updating section operable, when a depression of one of the instruction images (T1, T2, T3) is detected by the depression detection section, to update the cumulative number-of-times value of said depressed one of the instruction images stored in the cumulative number-of-times value storage section; and a change amount updating section operable to set the change amount associated with a first one of the instruction images (T1, T2, T3) whose cumulative number-of-times value stored in the cumulative number-of-times value storage section is a first cumulative number-of-times value, in such a manner as to become greater than the change amount associated with a second one of the instruction images (T1, T2, T3) whose cumulative number-of-times value stored in the cumulative number-of-times value storage section is a second cumulative number-of-times value smaller than the first cumulative number-of-times value; wherein the change amount updating section is configured to update the change amount associated with each one of the instruction images in such a manner as to become smaller as the cumulative number-of-times value of the depression detected by the depression detection section becomes smaller.