Abstract: A warning system for a vehicle obtains image data by three-dimensionally recognizing a road extending ahead of the vehicle and traffic conditions, decides that driver's wakefulness is on a high level when there is any one of psychological stimuli to the driver or that driver's wakefulness is on a low level when there is not psychological stimulus to the driver, estimates the possibilities of collision and off-lane travel, and gives the driver a warning against collision or off-lane travel when there is the high possibility of collision or off-lane travel.