PURPOSE: To mask the arbitrary range of an original without using a shielding sheet by providing an alteration means altering the transmission factor of light at a prescribed position in a main scanning direction.

CONSTITUTION: A transparent substrate 23 in narrow width is provided on an optical axis 22 connecting a light source 16 and a reflecting mirror 17 and at the upper part of original covering glass 15 in the main scanning direction vertical to an auxiliary scanning direction. The transparent substrate 23 is constituted by two glass plates, LCD sandwiched by the plates and a light transmission element consisting of an electro-chromic element. The light transmission element is constituted by plural elements, and the transmission factor of the light can be controlled by selectively impressing prescribed voltage on the prescribed element. When the transmission factor is made near 0%, light is shielded. When light is shielded at every position of the auxiliary scanning direction in accordance with stored data of RAM, the prescribed range of the picture of the original 12 is masked and only the picture in the prescribed range can be extracted.