A radar unit emits beams, and receives a reflection beam reflected by an object. A position of the object relative to a vehicle and an attribute of the object are recognized based on the emitted beams and the reflection beam. A coordinate position of the vehicle in an absolute coordinate is calculated based on a traveling amount of the vehicle, and a coordinate position of the object is calculated based on the calculated position of the vehicle and the position of the object relative to the vehicle. A road environment of the vehicle is recognized based on the coordinate positions and the attribute of the object.