1. An external recognition apparatus comprising: a three-dimensional distance measurement device configured to acquire distance information in a three-dimensional space in a predetermined region which is under a hydraulic shovel and which includes a region to be excavated by the hydraulic shovel; a plane surface estimation unit configured to estimate a plane surface in the predetermined region based on the distance information; and an excavation object region recognition unit configured to recognize the region to be excavated in the predetermined region based on the plane surface and the distance information.