PURPOSE: To enable to flold an A2 paper into Z-folded A4 and an A3 paper into two in a paper folder for transfer papers by providing a width-shift mechanism, a cross-folding mechanism, and a double/reverse folding mechanism on the downstream side of a feed direction folding mechanism.

CONSTITUTION: For Z-folding a paper A2, the paper is made to pass through the first pocket 7 with the first stopper 17 at a separated position from the first gate 8. It is sent to an upper feed mechanism 32 along a downstream guide 31, shifted in its width by a feed roll 37 and a guide 38, and conducted into a lower feed mechanism 33 along a downward guide 41. At this stage, it is folded into two by the first positioning piece 42 and a blade 52, conducted into the third pocket 76 via folding/feeding rolls 50 and 50', brought into contact with a stopper 79, and Z-folded at a nip part 80. Meanwhile, for folding an A3 paper into two, the first stopper 17 of the first pocket 7 is set at the second position to stop the introduced paper, and the paper is bitten at a nip part 10, and issued from a nip part 15.