A 3D-object detecting apparatus may include a detection-image creating device configured to detect a 3D object on an image-capture surface from an image captured by an image-capture device and to create a detection image in which a silhouette of only the 3D object is left; a density-map creating device configured to determine the 3D objects spatial densities at corresponding coordinate points in a coordinate plane on the basis of the detection image and mask images obtained for the corresponding coordinate points on the basis of virtual cuboids arranged for the corresponding coordinate points and to create a density map having pixels for the corresponding coordinate points such that the pixels have pixel values corresponding to the determined spatial densities; and a 3D-object position detecting device that detects the position of the 3D object as a representative point in a high-density region in the density map.