A thermal master making device and a thermal printer including the same are disclosed. A thermistor senses ambient temperature around a thermal head. A correcting device corrects the amount of heat to be generated by the thermal head, i.e., the duration of energization at least two times during a single master making operation. This configuration reduces a change in the perforation conditions of a thermosensitive medium ascribable to the heat accumulation characteristic of the head. The printer achieves high resolution, high-speed master making and space saving.