A printing apparatus is provided which uses, as a print head, a thermal head having heating elements arrayed in a line perpendicular to the traveling direction of a printing medium. Correspondingly pixel data, at either end, or near the end, of each line of image data going to be printed, data on heat storage in the thermal head (108) is calculated for each line on the basis of data on heat storage in the print head for a preceding line, and the data on heat storage in the print head for each line is compared with predetermined-temperature data. When any of the stored-heat data is larger than the predetermined-temperature data, energy to the heating element (113) is decreased. The image data is printed on the printing medium (104) with the energy for application to the heating element (113) being kept decreased. Thus, even when high-speed printing is done, it is possible to prevent a high temperature from developing at either end of the thermal head, to thereby preventing print-density nonuniformity from resulting in a printed image.