PURPOSE: To enable to control the density of printing by providing a density controller means capable of controlling the density of printing by a printing means to a specified gradation according to the output from a comparator means.

CONSTITUTION: In the embodiment of the present invention, the higher the density of printing, the greater the number of signals output from a picture reader 17, and when there takes place printing with the density higher than normal, a comparator 19 outputs high-density signal to a heating voltage control circuit 20, subsequently according to the high-density signal, the heating voltage control circuit lessens the heating voltage to be applied to the heater of a thermal head 5, whereby the thermal head is heated less, thereby the quantity of ink which is melted away by the thermal head, for every one of dot, from the ink ribbon, is decreased, whereby printing with a proper density is assured, thereby high quality of printing is made available.