A machine-plate manufacturing device 30 includes a cylinder section 32 having an outer circumferential portion. A groove into which an engagement portion of the sheet is removably inserted is formed in the outer circumferential portion of the cylinder section 32. On the inner side of the outer circumferential portion of the cylinder section 32, magnetic attraction members 51 formed of a magnetic material are provided, and permanent magnets 53 are provided in such a manner that their orientation can be switched. Permanent-magnet switching means is provided to switch the orientation of the permanent magnets 53 between a magnetization position for magnetizing the magnetic attraction members 51 and a demagnetization position for demagnetizing the magnetic attraction members 51.