Patent ID: 8837997

Claim:
A belt driving device comprising: an endless belt; a plurality of entraining rollers which entrain the endless belt thereabout and which include a driving roller for revolving the endless belt and a tension roller capable of varying a tension of the endless belt; a shaft member supporting the tension roller for rotation and having opposite end portions which are independently movable in such a direction as to vary the tension of the endless belt; deviation transfer members fitted over the shaft member in such a manner as to adjoin respective of opposite ends of the tension roller in an axial direction of the tension roller, at least that deviation transfer member which is located on a downstream side in a deviation direction of the endless belt along the axial direction being movable in the deviation direction with deviation of the endless belt; and biasing members each having an elastic force which biases the shaft member in such a direction as to increase the tension of the endless belt and each including an acting end pivotally supported on an associated one of the deviation transfer members and a base end pivotally supported on an associated one of apparatus frames at a predetermined position, wherein the deviation transfer members include respective larger-diameter members which are larger in diameter than the tension roller and which are rotatably supported on the shaft member.