Abstract: An exposure control device of a copying machine is provided with a white member at an end portion of an original document holding surface of a platen so as to prevent adhesion of toners to a top end portion of the copying paper. While a scanning optical system moves from the scan start point to the border between the original document and the white member, sufficient light quantity to prevent fogging of the image of the white member is supplied by the exposure lamp. The light quantity of the exposure lamp is changed to a suitable value corresponding to the original document in response to a signal for detecting the border.