Electrostatic copying apparatus with means for preventing contamination of reverse side of copying medium

Claim 1

An electrostatic copying apparatus which comprises: an image forming body forming a toner image on the surface thereof; a transfer device for transferring electrostatically the toner image formed on the surface of the image forming body to a copying medium; and image forming means for forming an actual image on the surface of said image forming body over a length corresponding to the width of said copying medium which extends in a direction orthogonal to a direction of the supply of said copying medium, said transfer device includes a rotatable transfer roller which faces said surface of the image forming body for selectively transferring at least two different sizes of said copying medium, a drive means for moving said transfer roller to contact with the image forming body for such a period as to feed the copying medium for a distance equal to the length thereof in the feeding direction while keeping the copying medium in contact with said image forming body, and detecting means for detecting the length extending in the width direction of said copying medium supplied to produce a signal representative of the detected width, said image forming means includes a charger disposed facing the surface of said image forming body on which an image is formed, in said width direction, which responds to the detection signal from said detecting means to charge said image forming body over the length corresponding to the width of said copying medium, said charger is provided with at least two charging wires with the lengths corresponding to the widths of said copying mediums supplied and said charging wires selectively effect corona discharge in response to the output signal from said detecting means.