1. A medical image diagnosis assisting apparatus, comprising: a lung field area extraction means for extracting a lung field area from a three-dimensional medical image representing a chest region of a subject; a branch structure area extraction means for extracting a branch structure area from the three-dimensional medical image; a lung field local sub-area estimation means for dividing a branch structure local area representing a portion of the branch structure area into a plurality of branch structure local sub-areas and estimating a lung field local sub-area in the lung field area functionally associated with each divided branch structure local sub-area based on the branch structure area; a pulmonary evaluation value obtaining means for obtaining a pulmonary evaluation value of pulmonary function and/or morphology in each estimated lung field local sub-area; and a display control means for displaying, in a morphological image representing morphology of at least a portion of the branch structure local area generated from the three-dimensional medical image, the pulmonary evaluation value in each lung field local sub-area functionally associated with each branch structure local sub-area in the morphological image superimposed such that correspondence relationship between the pulmonary evaluation value and the branch structure local sub-area in the morphological image is visually recognizable.