ECU AND LANE DEPARTURE WARNING SYSTEM

The present invention proposes an ECU and a lane departure warning system capable of improving safety of all traveling vehicles including a host vehicle by using an environment sensor to warn another vehicle about departure of the other vehicle from a lane. An ECU () detects the departure from the lane. The ECU () determines whether another vehicle () leaves the lane on the basis of a detection signal from an environment sensor (), and visually or aurally warns the other vehicle () in the case where the other vehicle () leaves the lane.