Image forming apparatus including transfer belt having first and second image transfer surface planes arranged at an angle, and plural image bearing members facing same

An image forming apparatus includes a plurality of image bearing members, each for bearing an image, a transfer belt onto which images on each of the image bearing members are transferred, and a transfer device for transferring an image on the transfer belt onto a transfer material. When images borne on the plurality of image bearing members are sequentially transferred onto the transfer belt so as to form superposed images, such superposed images simultaneously are transferred onto the transfer material. An angle made by a first surface plane of the transfer belt which at least one of the plurality of image bearing members faces and a second surface plane of the transfer belt which image bearing members other than the at least one image bearing member face is substantially a right angle.