1. A gradient estimation apparatus comprising: a feature point extracting unit configured to extract feature points on an image captured by an imaging unit; an object detecting unit configured to detect image regions indicating objects from the image captured by the imaging unit; and a gradient calculating unit configured to calculate the gradient of the road surface on which the objects are located, based on the coordinates of the feature points extracted by the feature point extracting unit in the image indicating the object detected by the object detecting unit and the amount of movement of the coordinates of the feature points over a predetermined time.