A belt transporting device for circulatingly transporting an endless belt, which is in use with an image forming apparatus, such as copying machine or a printer. The belt transporting device includes a plurality of tension rolls, an endless belt laid on the tension rolls, the endless belt having a belt-end edge part protruding from an end of one of the tension roll and a guide member provided in the vicinity of the endless belt. The guide member comes in contact with the belt-end edge part so as to bend the belt-end edge part in a tapering-off direction. The guide member regulates the shape of the belt-end edge part so that a rotary peripheral length of the belt-end edge part becomes smaller than that of an area where a rear side of the endless belt is in contact with the tension roll.