A predetermined structure repeatedly branching from an origin and extending in directions away from the origin in such a manner to become wider is extracted, as a candidate of a tree structure defined by a plurality of nodes including a root node corresponding to the origin and a plurality of edges, from medical image data. A tree structure is created by reevaluating the definition of the tree structure, with respect to each of the plurality of nodes defining the candidate of the tree structure, by using a cost function that weights a probability that the plurality of nodes are connected to each other by evaluating a relationship between each of the plurality of nodes and the root node based on a geometric characteristic that the predetermined structure repeatedly branches from the origin and extends in directions away from the origin in such a manner to become wider.