PURPOSE: To inexpensively obtain a printing result of high quality by measuring the resistance values of a plurality of heating elements and controlling the applying time widths of the voltage applied to the heating elements on the basis of the measured resistance values of the heating elements.

CONSTITUTION: A resistance value measuring part 101 measures the resistance values of the respective heating elements of a thermal head 7 and a printing control part 105 sets voltage applying times of voltage applied to the heating elements on the basis of the resistance values of the heating elements measured by the resistance value measuring part 101. A printing density control part 103 sends out a control signal controlling strobe signal width to a strobe signal control part 102 on the basis of the resistance value at every heating element read by the resistance value measuring part 101 so as to uniformize the generation quantities of heat of the heating elements. A gradation printing control part 104 changes the generation quantities of heat by controlling signal width with respect to the strobe signal control part 102 on the basis of the resistance values of the heating elements to perform gradation printing.