1. An object detection apparatus comprises: an overlapping area acquisition unit which acquires a value related to an overlapping area indicating a high possibility of an object existence in a three-dimensional space, by using data generated by images acquired by a plurality of image acquiring units, which reflects the object image in the three-dimensional space by a back projection of the object area; an overlapping quantity acquisition unit which acquires an integral quantity of the value related to the overlapping area in a shape model which is a three-dimensional model concerning to a shape of the object as a detection target; an overlapping distribution acquisition unit which acquires a distribution degree of the value related to the overlapping area in the shape model of the detection target; and an object determination unit which determines whether an internal of the shape model of the detection target is an object or non-object using the integral quantity and the distribution degree.