PURPOSE: To fold zigzag a roll of form paper, by guiding the paper through delivery rolls to the position of last fold and reversing the tolls after detecting the transverse stitches.

CONSTITUTION: An end of rolled form paper a is drawn over guide rolls 10, 11, 12 and through a pair of rolls 6 to a position below a delivery conveyer 15. When a pulse motor 36 driven by a phototube 43 gives a swivel plate 40 a turn together with cranks 39, a detecting plate 42 which also makes a turn is separated from the lower side of the paper a and reaches the upper side. At the same time, a clutch 2 on the other side of plate 5 is activated to make a chain 20 travel, which transfers the plate 5 while a swash plate 7 swings. The delivery rolls 6 thus deliver the paper a to the folding position.