A vehicle-to-vehicle communication system (V2V) sends and receives vehicle information by wireless communication and assists safe driving. The present study investigated the activation timings of collision information support, collision caution support, and collision warning support provided by a V2V in an experiment using a driving simulator for four situations of (1) assistance in braking, (2) assistance in accelerating, (3) assistance in making a right turn, and (4) assistance in making a left turn at a blind intersection. The four situations are common scenarios of traffic accidents in Japan. Safety margins for collision information support and collision warning support were the time required for the driver to fully apply the brake pedal, while the safety margin for collision caution support was the time required for the driver to begin applying the brake pedal. The study investigated the effects of adding safety margins to standard activation timings. The standard activation timings referred to activation timings defined by V2V guidelines of the Japanese Ministry of Land, Infrastructure, Transport and Tourism. The effects of new activation timings were investigated in the experiment. Objective (based on the use of the accelerator and braking pedals) and subjective evaluations were made of the activation timings. As result, in the case of collision warning support, the appropriate activation timing of V2V is 2.0 s in all experimental conditions. The timing of 2.0 s means that the safety margin is added twice to the standard activation timing. The collision caution support has appropriate activation timing if the safety margin is added once to the standard activation timing under several experimental conditions. In the case of collision information support, the appropriate activation timing was the addition of one safety margin to the standard activation timing in all experimental conditions.