Patent ID: 8879931

Claim:
An image forming apparatus comprising: an image bearing member for bearing a toner image; a rotatable endless belt; a first driving member for rotationally driving said endless belt and in contact with an inner peripheral surface of said endless belt; a second driving member for rotationally driving said endless belt and in contact with an outer peripheral surface of said endless belt, wherein said second driving member is provided at a position where it does not oppose said first driving member via said endless belt; and a tension detecting unit for detecting a state of tension of said endless belt; wherein said tension detecting unit comprises: a movable device, in contact with said endless belt in a first region from downstream of said second driving member to upstream of said first driving member and in a second region from downstream of said first driving member to upstream of said second driving member with respect to a rotational direction of said endless belt, and capable of moving its position depending on the tension of said endless belt in the first and second regions; a member to be detected capable of changing its position in interrelation with the movement of said movable device; and a detecting device for detecting said member to be detected.