When the user presses an Alt key, the mode makes a transition to a property value switching mode and all annotations are made visible. At this time, the originally invisible annotations with the visibility properties set to invisible are drawn translucently. That is, a scanner name, a color bar, and a patient name which are not visible in a normal mode are drawn translucently. Thus, the user presses the Alt key, whereby the mode can be switched to the visible switching mode of drawing all objects, so that the user can promptly designate the annotation whose visibility property is to be changed and can smoothly conduct a medical diagnosis with an image.