To prevent a projecting part formed on an endless belt from running onto a supporting roller for supporting the endless belt even in the case an external force is applied on the endless belt, in a belt device where the endless belt is supported by a plurality of supporting rollers so that the belt can travel.

The belt device is provided with a rotating member 86 having the diameter which is coincident or nearly coincident with the diameter of the main body part 65B and arranged between the main body part 65B of a driving roller 65 and the projecting part 67B so as to be coaxial with the main body part 65B of the driving roller 65, and a supporting member 85 constituted of a member other than that for the main body part 65B of the driving roller 65, and for rotatably supporting the rotating member 86 at the installation angle of gradually coming close to the projecting par 67B when the endless belt 67 moves in an advancing direction, and the projecting part 67B and the rotating member 86 are made to come into contact with each other at a comparatively late time, then, components of force making the projecting part 67B run onto the rotating member 86 is hardly caused.