A drive device for a belt conveyor device includes a drive pulley, a first pulley, a second pulley, a support frame, and a drive motor. The drive pulley has a drive shaft direction length less than a plurality of previously set belt widths of the endless belt and has the driving shaft direction length being set to a same length regardless of the plurality of previously set belt widths of the endless belt. Axial lengths of the first pulley and the second pulley are set to the same length as the axial lengths of the head pulley and the tail pulley. The support frame is rotatably attached to the first pulley and the second pulley. The drive motor hung from a lower surface of the support frame in order for the drive pulley to be positioned at an approximately center portion in a width direction of the endless belt.