PURPOSE: To facilitate the adjustment of the tension to a chain by making a rotor abut on the chain and add the tension to it and moving a supporting member in a long hole so that the tension to the chain may be adjusted.

CONSTITUTION: Rotors 88 and 98 abut on the chain 106 for transmitting the driving force of a motor 80 to a conveying roller so as to add the tension. In the case of adjusting the tension, nuts 92 and 104 are loosened and the ends of shafts 86 and 87 are moved in the long hole, then the nuts 92 and 104 are locked again at a position where the necessary tension is obtained and the tension to the chain 106 is adjusted. Thus, the nuts 92 and 104 are locked to adjust the tension to the chain 106. The tension to the chain 106 is easily adjusted just by loosening the nuts 92 and 104 and moving the shafts 86 and 87.