To provide a plate making apparatus which minimizes the overlap amount of thermal heads and prevents the deterioration of the image quality of overlapping portions.

In the plate making apparatus 3, the heating element 18 of each end of the thermal heads 13a and 13b adjacent concerning the main scanning direction is arranged to provide the overlapping portions 21a and 21b to be at the same position concerning the sub-scanning direction. In the plate making apparatus 3 having a control means 33 which alternatively selects the heating element 18 of the overlapping portion 21a and the heating element 18 of the overlapping portion 21b synchronously with the transportation of a master 12 to the sub-scanning direction, drives the selected heating element, and controls it to complete the print of each line in the main scanning direction of the master 12 by driving each of the thermal heads 13a and 13b, the control means 33 controls the pixels 41a and 41b of the overlapping portions 21a and 21b to print in heat quantity equal to or smaller than the pixels 40a and 40b of other portions.