PURPOSE:To heat up a heating element to a desired temperature in a short time without the supply of excessive power to the heating element by a method in which a preliminary heating element formed on a base plate, a heating element formed on the preliminary heating element through an insulator layer, and a protective film formed on the heating element are provided, and the heating element is preheated by the preliminary heating element. CONSTITUTION:An adequate amount of current is supplied between electrodes 4 to heat up a preliminary heating element 3, and a heating element 6 is preheated to an extent that a thermal paper does not color-develop or the ink of a thermal transfer ink ribbon is not separated. In performing printing, current is supplied between electrodes 7 to heat up the element 6. The heating can thus be quickly attained to a desired temperature by the application of smaller amount of current than in the conventional cases. The life of the element 6 can be lengthened without burden of excess load to the element 6.