PURPOSE: To prevent burning of a display and reduce power consumption by detecting brightness around the display with a sensor and using its value for controlling a luminance signal.

CONSTITUTION: This device is constituted with a sensor section 10 which detects brightness around a display, a detecting section 30 which detects variation of the condition of the display, a time measuring section 40 which measures nonvariation time of the display condition, and a luminance signal control section 20 which controls a luminance signal by a value from the sensor section and a value from the time measuring section, the luminance signal control section reduces the maximum luminance level at every constant interval of time as far as the display condition is not varied.