The purpose of the present study was to analyze driver's behavioral pattern in traffic conflict situation using a driving simulation study and to develop a diagnosis system for the driver's behavior pattern based on driving performance data in simulated traffic conflict situation. In Study I, typical and representative driving conflict situations were determined by using an in-depth interview. In Study II, driver's collision avoidance behavior patterns under the various traffic conflict situations were analyzed in terms of drivers' response strategies and their effectiveness. The main results can be summarized as follows: First, the drivers tended to report traffic situations as conflicting in intersection rather than straight lane condition. Second, conflict avoidance effort using brake or both brake and steering wheel found to be more effective than using steering wheel alone in terms of various safety criterial such as speed at collision and number of collisions. Third, drivers performances such as collision avoidance and vehicle operations were better in traffic conflict condition of "cross-traffic-from-right" than "cross-traffic-from-right" or "opposing lane". Finally, a possible model of diagnosis system for driver's conflict avoidance behavior pattern under the traffic conflict situation was proposed and several implications of the study were discussed.