The invention relates to a width-adjusting device for conveyor corridor(s), comprising a wide gear-reduction mechanism connected to the frame (5) of said conveyor, wherein said mechanism is arranged between the control shaft (12) and the wall(s) of said corridor. The device includes: a final drive capable of reverse operation and consisting of said control shaft (12) in the form of an endless screw and of a toothed wheel (11); and a system for controlling at least one of the walls of said corridor, consisting of an endless screw (13) and a nut, the endless screw being mobile or fixed relative to said toothed wheel (11). The shaft (12) of the final drive is a flexible shaft having a long length and engaging with the tension-retaining system (20) for absorbing the pulling and pushing forces in the rotation direction thereof.