In the rotation drive mechanism used for the mechanical pencil, the cam structure is simplified, the number of parts is reduced, and the ease of assembling the rotation drive mechanism is secured. On the upper and lower surfaces perpendicular to the axial direction of the rotary cam 24 constituting the rotary drive mechanism 21, a plurality of cam surfaces 24a, 24b which are continuous in a circular ring shape are formed, respectively. The holder member 23 rotatably supporting the rotating cam 24 is formed by integrally forming an axially long elastic member 23b and having a small number of cam surfaces at the proximal and distal ends of the elastic member. The 1st and 2nd fixed cams 23c and 23d are arrange|positioned so that the upper and lower cam surfaces 24a and 24b of the said rotation cam 24 may be interposed. The rotation cam 24 is rotationally driven in one direction by retracting and advancing in the axial direction by the writing pressure received by the writing core, and is configured to transmit rotational motion of the rotating cam 24 to the writing core.
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