IMAGE FORMING DEVICE

PROBLEM TO BE SOLVED: To prevent soiling of edge surface and obtain a transfer image without any soiling in an image forming device provided with a contact type transfer device. SOLUTION: In this image forming device utilizing a negative-positive developing process utilizing a photosensitive body with potential by electrification of -800 V, developing bias: B against a photosensitive body part in an non image range corresponding to the space between piece of paper and the range from the leading edge of transfer paper to 15 mm is set to be -450 V which is lowered than the developing bias A: -550 V against normal image range. Thus, the absolute value of developing surface potential is made greater in the range in the non image range and the transfer paper leading edge 15 mm (output timing (2)) than at normal times (output timing (1)). Therefore, the soiling of the edge part of the transfer paper is prevented by preventing the sticking of surface soiling toner in that part.