Provided is a thoracic diagnosis assistance system. The system includes, an imaging unit, an extracting unit, a region dividing unit, an analysis unit and a display unit. The extraction unit extracts a lung field region from the plurality of successive image frames generated by the imaging unit. The region dividing unit divides the lung field region extracted by the extraction unit into a plurality of sub-regions and correlates the sub-regions among the plurality of image frames. The analysis unit performs an analysis of the sub-regions to calculate an inspiratory feature quantity and an expiratory feature quantity and to calculate a value of a ratio of the calculated inspiratory feature quantity to expiratory feature quantity and creates a histogram of the calculated ratio value. The display unit displays the histogram.