An assembling device, an assembling method and a manufacturing method of a driving belt, which can facilitate fitting of rings into a recess of an element to improve productivity of the driving belt.The driving belt V, in which two rows of rings 8a and 8b are accommodated parallel to each other in a recess 7 of a plurality of elements 1 interlinked annularly in a manner to situate the recess 7 to open to an outer circumferential side, and in which the rings 8a and 8b are held in an inner circumferential side of the protruding portions 9 formed on an opening end of inner walls 6 of the recess 7 to prevent detachment of the rings 8a and 8b from the recess 7, comprises: a ring holding member 8c for restricting a relative movement between the rings 8a and 8b aligned parallel to each other entirely in its length direction without being overlapped.