A backlight unit shortens the necessary time from the time immediately after the turn on to the time the emitted light is converged to a predetermined chromaticity while the quality of time-varying images is improved. Under the control of the backlight controller section, the Light-Emitting Diodes (LEDs), which are assigned to the respective light-emitting regions of the light-emitting surface, are driven to emit lights sequentially in the predetermined scanning light-emitting periods for the scan type lighting and the additional light-emitting periods in a single frame, responsive to the write scanning of an image signal to the LCD panel. The additional light-emitting periods are outside a corresponding one of the scanning light-emitting periods. In each additional light-emitting period, the LEDs emit light in synchronization with the supply of the optical leakage preventing signal (e.g., the black inserting signal) to the LCD panel.