1. An image display apparatus comprising: a display unit; a storage unit; and a processor configured to execute a process comprising: making the display unit display an image including a plurality of ruled lines; detecting coordinates designated by a user by an input operation on a display screen of the display unit, and to obtain a trajectory of the detected coordinates; and making the display unit enlarge a part of the image including the ruled lines by an enlargement rule selected based on an arrangement of intersections of the trajectory of the obtained coordinates and the ruled lines, and display the enlarged part of the image.