A thermal transfer printing apparatus has a thermal head comprised of a plurality of heating members aligned in line, each of the heating members transferring an ink to printing paper upon heating so as to form one dot, the thermal head moving relative to the printing paper and defining a pixel using m.times.n printing dots (m, n: positive integers). This apparatus further has multilevel dot pattern generating means for storing several binary dot patterns having predetermined dots of the m.times.n dot matrix, and for selecting, upon reception of an image signal indicating the density of each pixel, a binary dot pattern in accordance with the density of each pixel, determining multilevel data for each dot constituting the selected pattern in accordance with the density of each pixel, and generating the multilevel dot pattern in which the data for each dot is determined, and driving means, connected between the multilevel dot pattern generating means and the thermal head, for heating, in correspondence with a multilevel dot pattern, the heating member corresponding to the dot therein so as to transfer an ink onto the printing paper to form a dot pattern formed by dots having a size corresponding to the density of each pixel.