An image forming apparatus for electrostatically transferring a latent image formed on a photoconductive drum or similar image carrier to a recording medium held by a clamp drum or similar medium conveying member. The clamp drum has a cylinder or base made of aluminum, a conductive rubber layer covering the cylinder, and an overcoat layer covering the rubber layer and higher in electric resistance than the rubber layer. A bias voltage for latent image transfer is applied while the rubber layer is connected to ground. The photoconductive drum and clamp drum are pressed against each other by a predetermined force, the former following the rotation of the latter. The photoconductive drum is provided with a photoconductor having a great electrostatic capacity, thereby preventing the effective transfer voltage at the time of image transfer from increasing.