To provide an image display device capable of performing appropriate calibration regardless of the size or layout of pictures in a display means.

The image display device has a plurality of previously prepared layouts setting the position and size, etc. of an image display area in the display area of a display part 12. The image display area, set in a layout selected by a user via an operation part 13 from among the plurality of prepared layouts, is recognized by a control part 11, and a calibration image is displayed in the recognized image display area under the display control by the control part 11. After that, the brightness of the displayed calibration image is measured, and when the result of measurement of the brightness is inputted, a gradation conversion table is prepared based on the result of measurement. When a medical image is displayed for image reading, the gradation of the medical image is converted by using the gradation conversion table prepared according to the image display area, and the medical image is displayed in the image display area.