PURPOSE:To prevent density from becoming ununiform due to variations in a voltage applied to head elements, by providing a V-F converter for detecting the voltage applied to the head elements and converting the voltage into a frequency corresponding to the voltage, and controlling a strobe signal based on the frequency. CONSTITUTION:A V-F converter 17 detects a voltage applied to a bead element group 15, and converts the detected voltage into a frequency corresponding to the voltage. The frequency is counted by a counter 18, and a pulse, voltage or the like corresponding to the counted value is outputted to a strobe signal generating circuit 12. The circuit 12 determines a fall timing for the strobe signal according to the pulse width or voltage. Therefore, for example, when the number of head elements TH-1-TH-640 driven is increased the voltage applied to the elements is lowered, and the frequency outputted from the V-F converter 17 is lowered correspondingly. In such a case, the strobe signal generating circuit 12 retards the fall timing of the strobe signal, whereby the pulse width (d) of the strobe signal is incrased correspondingly, and the drop in the voltage applied to the head elements TH-1-TH-640 is compensated for.