In an apparatus having a document reading portion for reading an image of a document on a document platen, by reading an image of a document on a display screen using an area sensor, it's not necessary to set a document for reading on the platen so that the document is prevented from being left behind, and even when a document on the platen and the document sticks out of the platen to extend over the screen, it is possible to prevent the document on the screen is erroneously read. When detecting a document on the platen and detecting that an object on the screen does not have a standard size by the area sensor, a control portion of the apparatus controls so that the document reading portion reads the image of the document on the platen and the area sensor is prohibited from reading the image.