PROBLEM TO BE SOLVED: To provide an image display device by which an image area corresponding to a substance identical or similar to a set area of interest can be extracted on a CT image of a subject.SOLUTION: The image display device includes: a reconstruction means to reconstruct a monochromatic image corresponding to an image photographed by X rays of desired effective X-ray energy on the basis of projection data acquired by dual energy photographing a first acquisition means to acquire a relation between the effective X-ray energy and the representative pixel value of the area of interest in the monochromatic image of the effective X-ray energy a second acquisition means to acquire a relation between the effective X-ray energy and a representative pixel value of the image area in the monochromatic image of the effective X-ray energy for respective image areas other than the area of interest using the reconstruction means a specification means to specify an image area wherein the "relation" is similar to the area of interest and a display means to emphatically display the specified image area.
