Abstract: A document detecting apparatus for a copying machine, comprising a photo-sensor having a light projecting device which emits a measuring light from an inside of to an outside of a copying machine through an original glass plate, and a light receiving device which is installed at a position deviated from a path symmetric to an optical axis of said measuring light with respect to a normal line set up on a surface of the original glass plate and which is directed to receive a scattered light produced from the measuring light scattered at a surface of an original document placed on the original glass plate; and a microprocessor which judges whether or not the original document exists according to an intensity of a light measured by said photo-sensor.