To prevent a new belt from generating looseness by jointing one end of the new belt to the surface of an old belt and allowing run of the new belt along with the old belt by means of driving pulleys while being laid around an auxiliary pulley so that the new belt and the old bet run at the same speed.

A winding starter 8 of a new belt 3 is installed near a drive pulley 5 and an auxiliary pulley 7 is arranged behind a driven pulley 6. The end 9 of the new belt 3 is stuck to the surface 11 of an old belt 2 by means of adhesive, the drive pulley 5 is driven to run the old belt 2 and one end 9 of the new belt is moved to the vicinity of the auxiliary pulley 7. The one end 9 of the new belt is peeled up to be laid around the auxiliary pulley 7 and the end 9 of the new belt is stuck to the surface 11 of the old belt 2 again. The drive pulley 5 is driven again so that the one end 9 of the new belt is moved near the winding starter 8 and certain positions of the old belt 2 are cut to remove the belt. Subsequently, the new belt 3 is detached from the auxiliary pulley 7 and one end 9 and the other end 10 of a new belt are jointed together.