In this study, we analyzed the physiological characteristics of elderly drivers when they met an unexpected event like a sudden stop by the car in front or cut in lane while driving on the highway. Electroencephalogram (EEG), electrocardiogram (ECG), Galvanic skin response (GSR), and skin temperature (SKT) were measured and analyzed from drivers during driving using a driving simulator. In this experiment, 20 elderly people (males, 65.6±5.0 years old) who have driving experience more than 10 years participated. As a control group, twenty young male adults (26.3±2.0 years old) in twenties whose driving experience was over 3 years. All subjects performed practice driving about for 10 min to adapt to the driving simulator before the main test. Driving speeds given to subjects were 50, 70, 90, 110 km/h. Unexpected events were repeated twice. As a result, compared with young drivers, elderly drivers showed longer and greater cognitive strain while driving simulator. EEG analysis showed significant difference for relative spectrum power of β (β/(α+β+θ+δ)) between young and elderly drivers (p≺0.05). In case of the elderly drivers, relative spectrum power of β decreased more slowly after the events and a faster heartbeat was shown during the events than young drivers did. For SKT and GSR, elderly drivers' strain lasted longer than young drivers and they took also longer time to recover back to the normal state. In conclusion, elderly drivers showed the different physiological response under unexpected events and may need different guides for the safe driving.