A thermal transfer type printer prints a desirable dot pattern on a printing paper by heating heating cells within a thermal head which is pressed against the printing paper via a transfer ribbon, the surface of which is painted by thermal melting ink. A memory stores two kinds of current-on time data, each of which represent specific current-on time characteristics designating a relation between the current-on time and a surrounding temperature of the thermal head. This surrounding temperature is detected by a thermistor mounted on the thermal head. One of two current-on time characteristics can be arbitrarily selected, and desirable current-on time is read from the selected current-on time characteristics based on the detected surrounding temperature. Some heating cells are selected in accordance with the desirable dot pattern and the selected heating cells are heated for the desirable current-on time. In addition, the current-on time can be arbitrarily set longer or shorter by increasing or decreasing the value of the current-on time data, whereby the printing density can be arbitrarily varied.