A smallest enclosing body that encloses an abnormal region is set. A part of an organ, and the part belonging to the inside of an elliptic parabolic surface or a circular conic surface that circumscribes the set enclosing body, is extracted as a partial region. A region of a structure dominating the organ is extracted from the obtained medical image. A part of the organ, and the part including the abnormal region and being dominated by a part of the structure extending from a predetermined position in the extracted region of the structure toward the part of the organ including the abnormal region, is extracted as a dominance region. The partial region or the dominance region is determined as the excision region based on a predetermined excision region determination condition.