[Problem] To construct graph structures of bronchi in three-dimensional medical images with greater precision. [Solution] A continuous region-extracting unit (32) extracts continuous regions having pixel values that correspond to regions of air inside wide bronchi from a three-dimensional medical image in which bronchi are shown and a tree structure-constructing unit (33) constructs a tree structure that corresponds to the continuous regions. Meanwhile, a linear structure-extracting unit (34) extracts multiple linear structures that represent fragments of narrow bronchi by analyzing local dark-light structures near each point in the three-dimensional medical image. A tree structure-reconstructing unit (35) reconstructs a graph structure that represents the bronchi as a whole by connecting nodes that configure graph structures of wide bronchi with nodes that represent linear structures of narrow bronchi. When so doing, different cost functions are used in the sections where wide bronchial nodes and narrow bronchial linear structure nodes are connected and sections where linear structure nodes are connected to each other, and the cost function of the former sections is defined so that the sections with smaller changes in pixel value are more easily connected.Linvention a pour but de construire des structures graphiques de bronches dans des images médicales tridimensionnelles avec une précision supérieure. A cet effet, selon linvention, une unité dextraction de régions continues (32) extrait des régions continues ayant des valeurs de pixels qui correspondent à des régions dair à lintérieur de bronches larges à partir dune image médicale tridimensionnelle dans laquelle des bronches sont représentées et une unité de construction de structure arborescente (33) construit une structure arborescente qui correspond aux régions continues. Pendant ce temps, une unité dextraction de structure linéaire (34) extrait de multiples structures linéaires qui représentent des fragments
