1. An image display device comprising: an image obtaining unit for obtaining a three-dimensional volume image obtained by imaging a chest of a human body; an information obtaining unit for obtaining information about costal regions on one of right and left sides of the human body in the three-dimensional volume image, and costal regions on the other of the right and left sides of the human body or vertebral regions of the human body in the three-dimensional volume image, the costal regions and the vertebral regions having been recognized and labeled in the three-dimensional volume image; an image generation unit for generating a display image from the three-dimensional volume image using the obtained information, the display image being a two-dimensional image including first partial regions that show at least a part of at least two of the costal regions on the one of the right and left sides, and second partial regions that show at least a part of at least two of the costal regions on the other of the right and left sides or at least two of the vertebral regions, wherein different colors or patterns are applied to the first partial regions that show different ones of the costal regions on the one of the right and left sides, and the same color or pattern as that of each first partial region is applied to the second partial region that shows a costal region provided with a label indicating a costal bone located on the opposite side of and paired with the costal bone shown by the first partial region or a vertebral region provided with a label indicating a vertebral bone connected to the costal bone shown by the first partial region; a display unit for displaying an image; and a display control unit for displaying the generated display image on the display unit.