A wrong-way-travel warning device comprising a vehicle speed detecting part configured to detect a vehicle speed of a vehicle, a part configured to detect a position of the vehicle, an angle detecting part configured to detect an angle of a vehicular longitudinal direction of the vehicle relative to a lane marking if the vehicle speed of the vehicle becomes less than or equal to a predetermined value, and a warning part configured to issue a warning to an occupant if the position of the vehicle is on a main lane of a highway and if the angle becomes about 90 degrees, is provided.