PROBLEM TO BE SOLVED: To prevent a traffic accident attributable to reduction in drivers arousal level by determining a drivers state correctly.SOLUTION: When a driver starts to drive a vehicle, openness of the drivers eye is successively calculated. When the openness of the drivers eye is below the threshold for a predetermined period of time, it is determined that the drivers arousal level reduces and an audible alarm is output toward the driver (Step S401). Then detection of the drivers reflex to the audible alarm is tried (Steps S402, S403). As a result, unless the openness of the eye is found to surpass the threshold, it is determined that the drivers arousal level reduces and the vehicle driven by the driver is quickly stopped (Step S404). Thus, traffic accidents attributable to the reduction in the drivers arousal level can be prevented.
