To suppress a variation in density when large volume continuous printing is performed.

In addition to a head temperature sensor 34 for measuring the temperature of a thermal head 21, a platen temperature sensor 37 for measuring the temperature of a platen roller 37 is provided. Since the platen roller 37 is not provided with a cooling mechanism like the thermal head 21, the rising rate of platen temperature is higher than that of head temperature when a large volume (e.g. twenty sheets or more) is printed continuously. A voltage being applied to the thermal head 21 is corrected depending on the head temperature and the platen temperature measured by respective temperature sensors 34 and 37. Since thermal energy generated from the thermal head 21 is corrected, the variation in the density can be suppressed when large volume continuous printing is performed.