To extract boundaries of interlobar fissures, pulmonary segments, or the likes from a three-dimensional medical image of the chest at a high speed and in a high precision.

A region extraction apparatus comprises: a three-dimensional medical image acquisition part 10 for acquiring a three-dimensional medical image of the chest; a bronchial tube structure extraction part 11 for extracting a bronchial tube structure from the three-dimensional medical image; a divided lung area acquisition part 12 for dividing the bronchial tube structure on the basis of the branching of the bronchial tube structure and for acquiring a plurality of divided lung areas on the basis of a plurality of the divided bronchial tube structures; a distance image creation part 13 for creating a distance image based on distances between pixels other than the divided lung areas and each divided lung area on the basis of the plurality of the divided lung areas; and a boundary non-existing area extraction part 14 for extracting boundary non-existing areas which do not include boundaries of each divided lung area on the basis of the distance image created by the distance image creation part 13.