An adverse situation warning device includes a route data storing portion for storing a first route data of a host vehicle including a first geohash corresponding to a moving route of the host vehicle, a route comparing portion for receiving a second route data of a remote vehicle including a second geohash corresponding to a moving route of the remote vehicle, and for comparing the geohash of the first route data and the geohash of the second route data, and a warning output portion for outputting an adverse situation warning based on the comparison result.