PURPOSE: To enable to print efficiently and with high quality even at a place where temperature is low, by impressing a preheating voltage on a heating element to previously maintain the temperature of the element at least at a predetermined temperature at which a thermal recording paper does not form a color.

CONSTITUTION: A plurality of diodes D1WDn+1 and a plurality of transistors Tr1WTrn are connected to the heating element 3 of the thermal printing head. When printing, the heating element 3 is supplied with printind voltages for each part thereof sectioned by the diodes and the transistors. In the head, before starting printing or at blank parts in printing, voltages such as not to cause the pirnting paper to form a color are impressed on the element 3 by utilizing the diodes D1WDn+1 and the transistors Tr1WTrn, thereby maintaining the element 3 at, for example, about normal temperature. Accordingly, it is made possible to print efficiently and with high quality when printing by impressing printing voltages.