PURPOSE: To conduct printing having high picture quality even when noises are generated in a motor driver circuit by connecting a diode for preventing a noise reverse current into an electric line connecting a constant-voltage power circuit and the motor driver circuit while connecting a printing head between the constant-voltage power circuit in the electric line and the diode.

CONSTITUTION: A print head 20 and a motor driver circuit 31 are formed in constitution, in which the printing head and the motor driver circuit are noise- insulated by a diode 51 for preventing the reverse current of noises, and the diode 51 is interposed and connected into an electric line 15 connecting a constant-voltage power circuit 10 and the motor driver circuit 31 (30). A connection point T2 between the constant-voltage power circuit 10 of the electric wiring 15 and the diode 51 and the print head 20 are connected through a branch electric wiring 15h. Accordingly, even when noises are generated on the motor driver circuit 31 side, no noise intrudes into the print head 20 side. A discharge circuit 55 is mounted, and noises, a reverse current of which is prevented by the diode 51, are absorbed to the smoothing capacitor C, and consumed by a discharge resistor R, thus having no effect of noises on any section.