To provide the method and device capable of controlling a roll forming based on the weight of a workpiece in a forming device having two oppositely arranged forming rolls constituted so that at least its one roll is moved neare to away from another roll and two opposed growth control rolls having operation line perpendicular to the operation line of these forming rolls.

The annular workpiece 6 is rolled between two forming rolls 2, 4 which are oppositely arranged and two growth control rolls 22, 24 which are oppositely arranged and operated in the direction perpendicular to the operation lines of these forming rolls 2, 4. The workpiece 6 is roll-formed to the wall thickness in accordance with the weight by cooperation of the forming rolls 2, 4. The advance of the growth control rolls 22, 24 is also controlled in the position dependent on the weight of the workpiece 6.