Abstract: Upon depressing a knock rod in a state of writing of FIG. 8A, a cam protuberance 3b of a rotor turns rightward to assume a position shown in FIG. 8B. Upon removing a finger, the cam protuberance 3b turns sliding on a tilted surface, arrives at a position shown in FIG. 8C through a first vertical motion (distance d) and, further, arrives at a position shown in FIG. 8D through a second vertical motion (distance e). Here, a tilted surface of cam protuberance 3b comes in collision with a tilted surface of an inner cylinder cam 2b twice, and shocks are transmitted to a refill 7. By forming a step between the front half and the rear half of the tilted surface of the inner cylinder cam 2b, however, a distance of vertical motion of the cam protuberance 3b each time is shortened to decrease the shock of collision imparted to the refill each time.