To solve a problem or the link of a master conveying mistake or jamming without arriving at a nip of reversing roller pair due to a strong curl or roundness of a distal end of a master when the distal end of the master is floated at the master including the curl caused by a winding nature or the like of the master when the master is set or the like.

A platemaking apparatus 20 comprises a thermal head 26 for platemaking the master 22, a platen roller 27, tension roller pair 37 and reversing roller pair 38 for conveying an unplatemaking master 22 or a platemade master 22, and a master conveying route MR. The apparatus 20 also comprises a control plate 7 as a master floating preventing means for preventing the floating of the master 22 is provided on the route MR between the head 26 and a master storage means 30.