Image forming apparatus

An image forming apparatus comprising:

• a transfer belt adapted to allow a plurality of toner images of different colors to be sequentially superimposed and transferred onto a surface thereof or a recording sheet placed on said surface so as to form a color toner image;
• a plurality of image-forming units disposed along said transfer belt and each adapted to form a toner image with a corresponding one of said colors and transfer said toner image onto said transfer belt or recording sheet;
• a drive roller for rotationally driving said transfer belt;
• a tension roller for applying a tension to said transfer belt in cooperation with said drive roller, said tension roller being changeable in position in response to a biasing force;
• a speed detector for detecting a rotation speed of said tension roller and outputting a roller rotation speed signal;
• and
• a position adjustment mechanism for preventing occurrence of a relative displacement between said speed detector and said tension roller.