An image display device generates a temperature information image indicating, by a numerical value, a temperature of each pixel contained in a predetermined area including a position on a thermal image specified by a user, and causes a display to display the temperature information image while a temperature of a pixel corresponding to the position specified is displayed at a center of the temperature information image. The image display device sets a temperature range that has a predetermined temperature width and a center which is a temperature of a pixel corresponding to a position the temperature information image specified by the user, updates the temperature-color conversion information based on the set temperature range, regenerates the thermal image and the temperature information image based on the temperature-color conversion information updated, and causes the display to display the regenerated thermal image and the regenerated temperature information image.