1. An object region extracting apparatus wherein the apparatus comprises: storage means for storing a visual feature quantity of a whole region of a specific object, and a visual feature quantity of each of partial regions obtained by dividing said object so that each partial region has a similar visual feature; region dividing means for dividing an input image into segments each having a similar visual feature; partial feature quantity extracting means for extracting a visual feature quantity of each of said divided segments; partial matching means for calculating a degree of similarity between the visual feature quantity of said partial region and the visual feature quantity of said segment, performing partial matching processing that decides whether or not the calculated degree of similarity has a predetermined relationship with a first threshold, and when they have the predetermined relationship, defining said segment as a candidate segment constituting a portion of the specific object; whole feature quantity extracting means for producing a combined region constituted by combining the candidate segments, and extracting a visual feature quantity of the produced combined region; and whole matching means for calculating a degree of similarity between the visual feature quantity of said whole region and the visual feature quantity of said combined region, and deciding that said combined region is a region similar to the specific object when the calculated degree of similarity and a second threshold fulfill a predetermined relationship, wherein said partial matching means performs said partial matching processing by selecting a visual feature quantity of each of said partial regions and said segments in a descending order of an area thereof, which are acquired along with the visual feature quantity, and selecting a visual feature quantity of a partial region having a next smaller area and a visual feature quantity of a segment having a next smaller area when said candidate segment is detected.