An object of this invention is to prevent an increase in energy applied to a heating element and prolong the service life of a printhead even when the temperature of the printing element having a negative temperature coefficient rises and the resistance of the heating element decreases upon controlling a switching element for controlling a current flowing through the heating element so as to make energy as constant as possible. For this purpose, a printhead having a plurality of heating elements connected to a common power supply comprises: a switching element which is series-connected to the heating element and controls driving of the heating element at a voltage applied to a control terminal; a constant voltage source using a common power supply as a reference; a wiring resistance generated at a connection wiring line serial-connected to the heating element; and a voltage control circuit which controls to make the potential difference between both ends of the wiring resistance equal to the voltage of the constant voltage source when driving the heating element. Then, a current flowing through the heating element is made constant without any influence of the temperature of the heating element.