1. An image display apparatus for processing externally acquired display data and displaying an image based on the processed display data, wherein: the display data contains the image and a control script that defines at least a first function of displaying the image; the image display apparatus comprises: basic function executing means for executing a basic function program called from the control script, the basic function program being stored in a basic function program storage section; and control script executing means for controlling the basic function executing means according to the control script so as to perform the first function being defined by the control script, the control script further defines a second function which the image display apparatus performs while the image is being displayed by the first function, and the control script executing means controls the basic function executing means according to the control script so as to execute the second function.