Tree structures corresponding to a first linear structure and a second linear structure are constructed from medical image data including the first linear structure and the second linear structure, each repeatedly branching from an origin and extending in directions away from the origin in such a manner to become wider. Each of a first root node corresponding to a root node in the first tree structure and a second root node corresponding to a root node in the second tree structure is connected to each node, based on the characteristic that each of the first and second linear structures repeatedly branches from the origin and extends in directions away from the origin in such a manner to become wider, by using, with respect to each node, a cost function that weights a cost representing a probability of connection of each of a plurality of edges connectable to each node.