Abstract: A printing mechanism 1 including a mandrel 2, and a tubular sleeve 3; wherein the mandrel comprises a main body and sleeve support members 6, a plurality of the sleeve-support members being arranged on the main body at intervals in the axial direction; and wherein the sleeve-support member has a plurality of arm portions 7 extending radially so as to support the sleeve from an inside thereof, and moving mechanisms 8 for moving tip vicinities of the arm portions inward/outward in the radial direction; and wherein the sleeve-support member has an interlock mechanism 9 for synchronously driving each moving mechanism of the sleeve support members, the tip vicinities of the arm portions being engaged with the inner surface of the sleeve or released from the engaged inner surface of the sleeve by the synchronous motion of the tip vicinities of all arm portions inward/outward with the interlock mechanism.