1. Background Vehicle to vehicle communication system (V2V) can send and receive the vehicle information by wireless communication, and use as a safety driving assist for driver. In particular, it is investigated to clarify appropriate activation timing for assist levels of (a) collision information, (b) collision caution and (c) collision warning. This study focused on the activation timing of collision information, caution and warning with V2V. The experiment carried out with a driving simulator, and this study investigated an effective activation timing for three assist levels. 2. Experimental method The experimental scenario had four situations of (1) “Assist for braking”, (2) “Assist for accelerating”, (3) “Assist for right turn” and (4) “Assist for left turn” in blind intersection. These were set on the basis of data of traffic accidents in Japan. The activation timings of three levels were based on TTI (Time to Intersection) and TTC (Time to Collision). Experimental parameter of activation timings referred to activation timings defined by Japanese V2V guidelines of the ministry of transport. Activation timings for collision information and warning used a time that a driver completes to operate the brake pedal. Also, a time that a driver starts to operate the brake pedal was applied to the activation timings for collision caution. This study investigated the effect of adaptation methods of this new activation timings by the experiment. Evaluation methods adopted the objective (accelerator and braking pedal works) and the subjective. 3. Conclusion The appropriate activation timings before approaching intersection of (1), (2), (3) and (4) were as follows; in case of collision information, (1), (2) and (3) were 5.1[s]. (4) showed 3.7[s]. In case of collision caution, (1) was 4.0[s], (2) was 2.4[s]. (3) and (4) were 3.2[s]. In case of collision warning, the all situations were 2.0[s].