To provide a paper guide device for a folding machine of a rotary printing machine in which the occurrence of a dog ear can be prevented by preventing the flapping and the rubbing of a signature, and which can flexibly deal with various kinds of paper qualities and paper thicknesses even at the time of the high speed operation of the rotary printing machine.

In the paper guide device 15' for a folding machine of a rotary printing machine, the gripping folding of a signature 7 is conducted by the cooperation of a thrusting barrel 3 equipped with a thrusting spatula 8 and a gripping barrel 10 equipped with a gripping spatula 9. The paper guide device 15' is provided in the vicinity of a portion where the gripping folding is conducted, and the high velocity flow of air along a required moving route when the front half 7A of the signature supported by the thrusting barrel 10 moves toward a gripping barrel 10 by pulling with the gripping barrel 10 is generated so that the front half 7A of the signature 7 is guided by the high velocity flow of the air and is moved toward the gripping barrel 10.