Abstract: An obstacle warning system for a vehicle includes a distance measuring device for emitting a transmission wave or laser light in a given angular range in a direction of a width of the vehicle in a scanning manner, and for detecting a distance between the vehicle and an obstacle in correspondence with a scan angle on the basis of a reflected wave or reflected light from the obstacle. A relative position calculating device calculates a relative position of the obstacle with respect to the vehicle on the basis of the distance detected by the distance measuring device and a corresponding scan angle. A radius calculating device calculates a radius of an estimated relative curved path of the vehicle with respect to the obstacle on the basis of relative positions of at least two points of the obstacle which are calculated by the relative position calculating device.