To provide an output compensation gear so cam-controlled as to select freely the laws of motion for a front gripper.

An output compensation gear is cam controlled for a sheet paper acceleration device formed of a front gripper 1, and the acceleration status of the front gripper is regulated by a one-rotation type control cam, and two compensation masses 21 and 22 disposed facing each other on the diameter and supported revolvably are provided, and the motion of revolution of the compensation masses 21 and 22 are controlled by control cams 23 and 24 attached respectively on the compensation masses 21 and 22.