Paper passes through the 1st folding area [A] without any treatment and bumps agianst the 2nd stopper [B] to make an arch in the paper. With this arch, the paper is fed into the 2nd-fold roller nip and the 1st fold is made. Then the paper bumps against the 3rd stopper [C] where paper is fed into to form the 2nd fold. As a result, a Z-fold is formed.