To provide a printing plate manufacturing apparatus capable of performing a stable printing plate manufacturing which does not depend on an uneven condition of a film of a master.

On the master 4 made by sticking a thermal film 3 on a porous supporting body 2, the reflectance of the film is measured by a reflection type optical sensor 10 before a printing plate manufacturing. When the optical reflectance is smaller than the standard, a controlling means controls a TPH (thermal print head) so that the energy outputted when the TPH 7 is driven is outputted much in accordance with the degree of smallness. The master is thermally processed into a printing plate by the TPH by a controlled energy while it is pinched and delivered by a roller 5, a platen roller 8 and the TPH. A good printing plate manufacturing is performed by an energy corresponding to the degree of the unevenness of the film.