To convey and discharge each of paper sheets smoothly and in the best condition even when the paper sheets are folded into various forms with different lengths in the conveying direction after folding, to simplify the whole conveying path, and to reduce the cost by reducing the number of parts.

The paper folding device is provided with a paper folding mechanism 3 folding the paper sheets P conveyed from a paper sending-in port 2i, and a discharging/conveying path 4 conveying the folded paper sheets P, which are sent out from the paper folding mechanism 3, to a paper sending-out port 2e. The device is further provided with: an outside paper-discharging mechanism 5s discharging the folded paper sheets P, which belong to a group in which the length in the conveying direction after folding is longer, to the discharging/conveying path 4; and an inside paper-discharging mechanism 5i discharging the folded paper sheets P, which belong to a group in which the length in the conveying direction after folding is shorter, to a plurality of paper stackers 8as, 8bs arranged at the positions corresponding to a plurality of paper sending-out positions Xa, Xb of a fold processing part 7.