An image display apparatus includes a display device and a computer configured to execute a program to cause the computer to serve as a display controlling part. The display part displays a first CT image and a second CT image simultaneously. The first CT image and the second CT image represent the same object but taken in different time periods. The display controlling part performs: displaying the first and second CT images simultaneously on the display device according to a first display mode; determining a target portion designated in the first CT image; and changing a display mode of a corresponding portion of the second CT image from the first display mode into a second display mode, the corresponding portion corresponding to the target portion designated in the first CT image.