A belt driving device includes an endless belt, a tension roller, a shaft member, deviation transfer members, and biasing members. The deviation transfer members are 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. Of the deviation transfer members, at least that deviation transfer member which is located on a downstream side in a deviation direction along the axial direction is movable together with the endless belt along the shaft member. Each of the biasing members has 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.