1. An image display apparatus comprising: a display unit capable of displaying a plurality of tomographic images or at least one plain image of a target object; a switching determiner configured to determine whether to switch the display on the display unit; and a display controller configured to control the display unit; wherein the display controller is capable of switching the display on the display unit to the display of tomographic images in sequence or to the display of a plain image, in case that the switching determiner determines to switch the display on the display unit, the display controller controls the display unit to display an image, which is different in kind from the image displayed on the display unit, instead of the image displayed on the display unit, in case that the plain image is displayed on the display unit, the display controller controls the display unit to display a sequence of a tomographic image, a plain image, and a tomographic image, instead of the plain image displayed on the display unit, using a tomographic image, which is displayed in a preceding order to the plain image displayed on the display unit, wherein in case that the display controller controls the display unit to display tomographic images in sequence, the display controller controls the display unit to display a plain image each time that the display unit displays a prescribed number of tomographic images in sequence.