It is an object to provide a driving support system and a display device suitable for the driving support system. According to the driving support system, change in driver's mental and physical conditions can be caught instantaneously and a warning light emission display is given within the forward sight of the driver in order to call the driver's attention. A light emitting device of the driving support system can display a far side of the display. A display may be switched between a transmission mode and a non-transmission mode by adjusting a movable polarizer.