In an obstacle detection system for a vehicle which has a radar having an electromagnetic wave transmission device and a reflected wave reception device, the electromagnetic transmission device transmits electromagnetic waves in a direction in which the vehicle is traveling, and the reflected wave reception device receives reflected waves produced when the electromagnetic waves transmitted from the electromagnetic wave transmission device are reflected by an object present in the traveling direction of the vehicle. The system detects obstacles present in the traveling direction of the vehicle based on the result of a radar search operation, and it is possible to identify only those objects detrimental to the traveling of the vehicle as obstacles. An obstacle decision device decides whether or not the object detected by the radar is an obstacle, by using the detected value determined by a vehicle speed detection device which detects the speed of the vehicle, the calculated value determined by a relative distance calculation device that calculates a relative distance to the object present in the traveling direction of the vehicle based on the result of search operation by the radar, and the calculated value determined by an overlap calculation device that calculates an overlap in the width direction of the vehicle between the vehicle and the object according to the result of the search operation by the radar.