Image forming apparatus having endless belt tension detection

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, provided at a position different from a position of said first driving member with respect to a rotational direction of said endless belt, for rotationally driving said endless belt and in contact with an outer peripheral surface of said endless belt;
• a tension roller, provided in contact with the inner peripheral surface of said endless belt, for applying tension to said endless belt by being urged by a spring;
• a tension detecting unit for detecting a state of tension of said endless belt;
• and
• a controller for controlling a rotational speed of said second driving member,
• wherein a driving force applied from said second driving member to said endless belt is smaller than a driving force applied from said first driving member to said endless belt,
• wherein said tension detecting unit includes an optical sensor, opposing said tension roller via said endless belt, for measuring a distance to the outer peripheral surface of said endless belt, and
• wherein said controller controls, on the basis of a detection result of said optical sensor, the rotational speed of said second driving member.