The invention provides an auxiliary unit (10) for a folding-sizing machine and a relevant folding-sizing machine. The folding-sizing machine has a roller transmission system (12) driven by a motor. The auxiliary unit comprises a horizontal flat surface (11) and a motor-driven transmission belt (15) that moves on the flat surface (11) in a parallel manner. A hook device (16) is mounted above the flat surface (11) and is provided with a hook (17). The hook can move downward toward the flat surface (11) and be connected to a paper board sheet material (D) that moves ahead on the belt (15). The hook can be lifted to be above the flat surface (11) so as to not interfere with the sheet material (D).