The invention concerns a device for winding/unwinding metal strips, in particular for steel bands, comprising a mandrel (4) mounted mobile in rotation in a bearing (4a), and serves to provide means for pivoting, seizing, centering and suppoting the mandrel (4) of the winding/unwinding device. Therefor, the invention is characterized in that the bearing of the mandrel (4) is enclosed, on the outer ring (6) of the bearing, in an annular slot (7), and said outer ring (6) can be centered by means of a fixing element (8) capable of being closed inwards when the mandrel (4) is inserted, or can be freely mobile inside said annular slot (7) when the fixing elements (8) are returned outwards.