Apparatus for forming an annular product comprising a drum shaft (10) around a main shaft (8) tapering structures (12) each having axial slidability provided so that in response to a sliding movement of the tapering structure (12) the drum segments are each radially expanded or retracted. A stopper (13) for controlling the sliding movement of the tapering structure (12) is provided and the axial position of the stopper is regulated by a motor through a ball screw mechanism disposed in the main shaft (8). Thereby, settings and changes of circumferential length of the drum (14) to determine the length of the annular product are easily and certainly achieved. <IMAGE>
