An image forming apparatus includes an image bearing member for bearing a toner image; an endless rotatable intermediary transfer belt onto which the toner image is to be transferred from the image bearing member; a transfer device disposed at a position in which the transfer device opposes the image bearing member through the intermediary transfer belt, the transfer device including a sheet member surface-contacted to an inner surface of the intermediary transfer belt and including an urging member for urging the sheet member toward the intermediary transfer belt; and a primary transfer voltage source for applying a voltage to the sheet member.