A road configuration identifying device properly identifies the road configuration around a user's vehicle. A reliability level indicating whether the traveling paths of other vehicles in an area behind the user's vehicle which are detected by a radar positioning system, which are obtained by tracking other vehicles using an other vehicle tracking section, and the traveling path of the user's vehicle are traveling paths along the same road configuration is calculated by using the velocity v, acceleration dv, angular velocity dθ, and the operation state of a direction indicator or the like of each vehicle. Then, the road configuration indicated by traveling paths having a high reliability level is predicted as the road configuration in the area behind the user's vehicle. A warning device evaluates the possibility of other vehicles colliding with the user's vehicle based on the road configuration of the area behind the user's vehicle predicted by the road configuration predicting section and the behavior of other vehicles tracked by the other vehicle tracking section, and warns of the possibility of collision if such another vehicle is present.