The invention provides an object detection device for a vehicle. A roadside object present at the side of a road traveled by a vehicle in question, and a preceding vehicle (S14, S16) traveling ahead of the vehicle in question at a predetermined speed or above, are detected on the basis of a group of points derived by projecting, onto a two-dimensional plane, reflection points obtained by transmitting an electromagnetic wave in the direction of advance of the vehicle in question; it is determined (S18, S20) whether the roadside object has moved toward the road within a predetermined time before and after the preceding vehicle has passed close to the roadside object when the preceding vehicle moves past the roadside object; and the roadside object is determined not to be an obstacle (S22) when the roadside object is determined to have moved toward the road. A roadside object is prevented from being mistakenly determined to be an obstacle that has entered the road traveled by the vehicle in question when an object is detected using an electromagnetic wave.