A backlight driving device including a light source array, a driving circuit and a scanning circuit is provided. The light source array includes backlight units electrically connected to scanning lines and driving lines. The driving circuit outputs driving signals to the backlight units through the driving lines, and the driving signals respectively includes driving pulses in different time intervals. The scanning circuit outputs scanning signals to the backlight units through the scanning lines, and the scanning signals respectively includes a start pulse in at least one of the time intervals. The start pulses of the scanning signals respectively correspond to the driving pulses in the same time interval, and drive the backlight units of the each row of the light source array in time-division.