PURPOSE: To eliminate the need for waste space by a radiator plate, etc., and to reduce power consumption by connecting a pair of heteropolar transistors at both ends of a solenoid and efficiently regenerating currents to a DC power by a diode for regeneration to the power supply.

CONSTITUTION: When bias currents are applied to a base electrode for a transistor Tr 3, the base currents of a Tr 2 flow through a collector and an emitter for the Tr 3 and a resistor 5 from a DC power 1. Power is applied to a solenoid 4 from the power supply 1. When the base bias currents of the Tr 3 are interrupted, back electromotive force is generated in the solenoid 4. Since back electromotive force is generated in positive polarity at a point B and in negative polarity at a point A, currents flow by the loop of the point B → a diode 7 →the power supply 1 → a diode 6 → the point A, and the back electromotive force of the solenoid 4 is regenerated to the power supply 1. Consequently, the ON-OFF time of the solenoid is controlled accurately. Accordingly, waste space is unnecessitated, and power consumption is reduced.