Patent ID: 8571428

Claim:
An image forming apparatus, comprising: at least one photosensitive member; a plurality of developing units to supply developer to the at least one photosensitive member so as to form a visible image; a transfer belt to transfer the visible image formed on the at least one photosensitive member to a printing medium, an inner surface of the transfer belt being rotatably supported by at least two rollers; at least one sensor to sense a mark formed on the transfer belt; and a supporting unit to support the transfer belt at a position corresponding to the at least one sensor so as to apply a tensile force to the transfer belt, wherein the supporting unit includes a first supporting portion and a second supporting portion arranged to support the transfer belt at a first supporting position and a second supporting position in a rotating direction of the transfer belt such that the first supporting position is upstream from a position on the transfer belt corresponding to the at least one sensor and the second supporting position is downstream from the position on the transfer belt corresponding to the at least one sensor.