Vehicle to vehicle communication system (V2V) can send and receive the vehicle information by wireless communication, and can use as a safety driving assist for driver. Currently, it is investigated to clarify an appropriate activation timing for collision information, caution and warning in Japan. This study focused on the activation timing of collision information (Provide objective information for safe driving to the driver) on V2V, and investigated an effective activation timing of collision information, and the relationship between the activation timing and the accuracy of the vehicle position. This experiment used Driving Simulator. The experimental scenario is four situations of (1) “Assistance for braking”, (2) “Assistance for accelerating”, (3) “Assistance for right turn” and (4) “Assistance for left turn” in blind intersection. The activation timing of collision information based on TTI (Time To Intersection) and TTC (Time To Collision). The objective evaluation was evaluated by driver’s actions, and the subjective evaluation was evaluated by participates about the activation timing and necessity for collision information. As the results, in each scenario from (1) to (4), an appropriate activation timings of collision information was (1) more than 6s before intersection, (2) more than 3.7s before intersection, (3) more than 5.8s before intersection, and (4) from 1.4s to 10.8s before collision. Considering about the relationship between activation timing and accuracy of the vehicle position, if the system has an error of the vehicle position, experimental participates evaluated the system as “ineffective”.