Abstract: A paper folder is disclosed, in which a drive motor and a crank mechanism supplied with power from the motor are not directly coupled together. Instead, they are secured to a common plate such that their respective shafts penetrate the common plate in a suitably spaced-apart relation to one another and coupled together by a belt. An adjusting screw mechanism is assembled in the crank mechanism to permit easy and accurate adjustment of the position of the paper folding knife. The device thus can be constructed as a belt drive unit type device, which produces less noise and is subject to less wear.