A driving device used in a paper separation mechanism includes an internal gear, an external gear sheathed around the internal gear, a shell of which an inner front face protrudes backward to form a hollow cylinder which the internal gear is sheathed around, an elastic element restrained between a front end of the internal gear and the inner front face of the shell, and a driving member rotatably on the rear of the shell. The driving device utilizes the cooperation of a guide block of the internal gear and a guide groove of spiral shape of the hollow cylinder, the cooperation of a locking arm of the shell and an outer ratchet of the external gear, the cooperation of a slope of the external gear and pushing blocks of the driving member to make a clockwise rotation angle of the driving member be greater than a counterclockwise rotation angle.