PURPOSE: To provide each oscillating gripper with a constant gripping pressure independently and ensure that all the oscillating grippers start opening simultaneously, by a method wherein oscillating grippers constituting paper gripping mechanism are oscillated by a specified mechanism.

CONSTITUTION: A set of paper gripping mechanism is constituted of a fixed gripper 25 and an oscillating gripper 26 on a gripper shaft 10. In a mechanism for oscillating the grippers 26, bars 30 are arranged between right and left projections 27 and 28 and in parallel to the shaft 10 with spacing H, a spring 31 is fitted in a hole E of each gripper 26, plates 32 are tightened by screws 33 to provide each gripper 26 with a constant gripping pressure independently, and the gap h between the bar 30 and the projections 27 are adjusted by adjusting screws 29 screwed to the projections 27, whereby the grippers 26 can be started to open simultaneously. Thus, an easy and accurate fine adjustment is effected without changing spring pressure.