PURPOSE: To reduce the power consumption of a group energizing switching means by regulating the voltage to be applied to the switching means in a manner to reduce their power consumption correspondingly to the setting of voltage applied to the head by the switching means.

CONSTITUTION: A voltage control circuit 15 comprises a control transistor 15-1 arranged in the line of supply voltage V2, the bias resistor 15-2 of the control transistor 15-1, resistor 15-4 and 15-5 of an error detector for detecting a voltage V2' applied to switching means 9-1 and 10-1, a Zener diode 15-6 for correcting the reference voltage, and a resistor 15-7 for setting the reference voltage. The resistors 15-4 and 15-5 and the Zener diode 15-6 are selectively determined to meet a condition that the voltage V2' is equal to the sum of a correct voltage to be applied to a group energizing voltage applying terminal S6, the saturated voltage the collector and the emitter of the transistor 9-1 and the saturated voltage between the base and the emitter of the transistor 10-1.