A three-dimensional medical image obtainment unit that obtains a three-dimensional medical image of a chest, a bronchial structure extraction unit that extracts a bronchial structure from the three-dimensional medical image, a divided lung region obtainment unit that divides, based on the divergence of the bronchial structure, the bronchial structure into plural bronchial structures, and obtains plural divided lung regions based on the plural divided bronchial structures, a distance image generation unit that generates, based on the plural divided lung regions, a distance image based on a distance between each voxel in an entire region excluding at least one of the plural divided lung regions and each of the plural divided lung regions, and a border non-existing region extraction unit that extracts, based on the distance image generated by the distance image generation unit, a border non-existing region, which does not include any borders of the divided lung regions, are provided.
