In Japan, many new technologies using Intelligent Transportation System (ITS) have been developed in order to reduce traffic accidents as well as to relief traffic congestion. Adaptive Cruise Control system (ACC) is one of the ITS technology to avoid vehicle collision and has been introduced gradually in Japan. The impact to a driver's behavior of installation of ACC to a single vehicle such as the technology for reducing collision could be evaluated by using a driving simulator. However, the impacts of ACC installation on traffic flow has not yet been evaluated because of difficulty of developing evaluation model such as including complexity of interaction among ACC and other vehicles' behavior. Thus, this study proposes to evaluate the impact of ACC installation on traffic safety by using a micro traffic simulation model. Since, conventional micro traffic simulation models can not represent the potential traffic accidents because the most of them control vehicles based upon the vehicle-following-theory which prevents occurrence of vehicles collisions. For this purpose, the micro simulation model was basically modified by adding a function of driving error and then detects conflicts or near miss situations emerged between vehicles on the simulation. Time Measured to Collision (TMTC) and Post Encroachment Time (PET) etc are tested as indicators to represent conflicts instead of actual traffic accidents occurrence. As the case study, this study demonstrates the impact of safety indicators by ACC installation on traffic flow with different installation rates and different flow conditions.