1. An image display device comprising: at least one processor configured to execute one or more programs to realize one or more functions of: a feature value calculating section which receives image data for a right eye and image data for a left eye, which together form 3D image data, divides one of the image data for the right eye and the image data for the left eye into a plurality of reference regions, detects, on each reference region, an amount of separation between the reference region and a region in the other image data corresponding to the reference region, calculates a parallax value positively correlated with the detected amount of separation for each reference region, and calculates an image feature value related to a brightness of the one of the image data for the right eye and the image data for the left eye on the basis of a brightness of such reference regions as have the calculated parallax value exceeding a predetermined threshold value that is set in advance; an expanding coefficient calculating section which calculates an expanding coefficient, which is related to brightness expanding processing performed on the image data for the right eye and the image data for the left eye, on the basis of the image feature value calculated by the feature value calculating section; a brightness expanding processing section which performs the brightness expanding processing on the image data for the right eye and the image data for the left eye on the basis of the expanding coefficient calculated by the expanding coefficient calculating section; and an image display section which displays an image on the basis of the image data for the right eye and the image data for the left eye subjected to the brightness expanding processing.