PURPOSE:To improve the printing quality of a thermal head, by making the number of heating elements being controlled through respective print signals uneven thereby suppressing uneven printing density caused by voltage drop of a common electrode or warping of the thermal head. CONSTITUTION:Upto third printing signals SB1-SB3 from the left end control five driving IC's respectively, while printing signals SB4, SB5 control four driving IC's respectively and printing signals SB6-SB8 control three driving IC's respectively. Consequently, level of current flowing through a common electrode decreases as the distance from the power supply source increases, and the voltage drop in the common electrode does not increase remarkably even if the distance from the power supply side increases. If a thermal head 32 is warped in a projecting shape, number of heating elements in the central portion is increased to reduce quantity of heat to be produced from a single heating element while the number of heating elements is decreased at the opposite ends to increase the quantity of heat to be produced from a single element.