To reliably carry a master without applying a load to machinery components or a motor even when making a large-sized printing plate.

In a printing plate making apparatus 20, a master is nipped between a platen roller 21a and a thermal head 23a, the platen roller 21a is rotated and the thermal head 23a is driven to perform thermal prepress while carrying the master. The apparatus includes a grasping means 22 which has a pair of grasping members 23 at least one member of which is arranged with the thermal head 23a and arranged in the circumferential direction of the platen roller 21a wound with the master, and has a pressure mechanism 25 which grasps under pressure the grasping members 23 from the surface opposite to the abutting surface on the platen roller 21a.