Patent ID: 7917071

Claim:
A transfer belt unit comprising: a belt-like intermediate transfer medium for temporarily supporting a toner image that was formed on the surface of a photoreceptor; and a transfer roller for pressing the intermediate transfer medium against the photoreceptor, characterized in that the intermediate transfer medium has the toner image transferred from the photoreceptor surface whilst moving along the surface of the photoreceptor, the intermediate transfer medium is formed to be no less than 30 μm and no more than 50 μm in average thickness, and, the transfer roller is arranged, along the moving direction of the intermediate transfer medium downstream with respect to the moving direction from the point where the intermediate transfer medium is in contact with the photoreceptor and which is arranged closer to the photoreceptor side, from the position on the tangent line passing the contact point where the intermediate transfer medium comes into contact first in the moving direction with the outer peripheral surface of the photoreceptor, so as to press the intermediate transfer medium against photoreceptor with a nip pressure ranging from no less than 9.8×10 −2 MPa and no more than 39.2×10 −2 MPa.