A blind spot specification unit (21) specifies a plurality of obstacles generating blind spots in an area around the perimeter of a vehicle. A discrete calculation unit (231) uses each obstacle specified by the blind spot specification unit (21), as a target object, and calculates the probability of the occurrence of a traffic accident at a target position relative to the positions of the target objects, as a discrete probability. A composite calculation unit (232) calculates, as a composite probability, the probability of the occurrence of a traffic accident at target positions relative to the plurality of obstacles, making said calculation from the discrete probabilities calculated by the discrete calculation unit (231).