Image forming apparatus having means to prevent image quality degradation

An image forming apparatus, comprising:

• a transfer belt onto which a toner image formed on an outer surface of a photosensitive medium is transferred, the transfer belt traveling along a predetermined closed path while being supported by a plurality of rollers;
• two rollers of the plurality of rollers disposed at an inner surface of the transfer belt so that a nip between the photosensitive medium and the transfer belt is maintained;
• and
• a guide unit disposed at the inner surface of the transfer belt facing the photosensitive medium to prevent vibration of the nip during a transfer operation,
• wherein a transferring bias voltage is applied to one of the two rollers to transfer the toner image from the photosensitive medium onto the transfer belt, and the guide unit is an electrical conductor that blocks an electric field between the photosensitive medium and the one roller to which the transferring bias voltage is applied, thereby facilitating the image transfer.