1. A vehicle periphery monitoring device comprising: an image capturing unit mounted on a vehicle and configured to acquire a captured image around a periphery of the vehicle by performing image capturing while the vehicle is traveling; an identification target area determiner configured to determine identification target areas from within an image area in the captured image acquired by the image capturing unit; and an object identifier configured to identify whether or not an object exists within the identification target areas determined by the identification target area determiner, wherein: the object identifier includes a first identifying unit for which a computation amount thereof required by an identification process for identifying the object is relatively small, and a second identifying unit for which a computation amount thereof required by an identification process for identifying the object is relatively large; and the identification target area determiner determines at least one of the identification target areas to be subjected to the identification process by the second identifying unit, by performing a clustering process in relation to position and/or scale with respect to plural area candidates extracted by the first identifying unit as areas in which the object exists, wherein the identification target area determiner divides the image area into a plurality of sub-areas, and determines the identification target areas by performing the clustering process in relation to position with respect to each of representative positions of the area candidates calculated in each of the sub-areas.