The invention concerns a forming device intended to form a bend in a corrugation, the forming device comprising: a bottom frame (4) having a planar mounting surface (6) intended to receive a sheet metal plate having a corrugation projecting relative to a planar portion of the sheet metal plate, a projecting counter-form (5) arranged on the mounting surface and intended to be accommodated in the corrugation, the projecting counter-form having a stationary portion (7) and a movable portion (8) that is hinged, relative to the stationary portion, about an axis perpendicular to the mounting surface, a top frame (34) arranged above the bottom frame, a press configured to lower the top frame towards the bottom frame, and a hollow upper die carried by the top frame between the top frame (34) and the bottom frame (4), the hollow upper die (36, 37) being arranged above the movable portion of the projecting counter-form.