PURPOSE: To detect the presence or absence of an original as well as the size of the original without disturbing the exposure route, by obliquely cutting the edge surface of the original placing contact glass and providing a light emitter and a light receiver opposite to the cut oblique surface of the glass.

CONSTITUTION: The edge surface of a contact glass 1 fixed to a frame 2 is cut obliquely, and a light emitter 3 and a light receiver 4 are provided opposite to the cut oblique surface. When no original is put on the glass 1, the light sent from the emitter 3 is divided to the component advancing upward after passing through the glass 1 and the component reflected regularly on the surface of glass. Both components are not reflected to the side of the incident optical path and thus not made incident to the receiver 4. When an original 5 exists on the glass 1, the light is divided to the component reflected regularly on the surface of the glass and the component reflected irregularly on the surface of original 5. A part of the light component reflected irregularly comes back to the incident surface, accordingly, the light is made incident to the receiver 4 to be converted into the electric signal.