To improve power source efficiency by allowing energy induced to another coil serially connected with a coil as a load and coupled by mutual inductance to regress through a diode to a power source when a switching element for turning on/off the power source for driving a coil is turned off.

A power source Vcc is connected with one end of a coil L1 being a load, and a transistor TR1 being a switching element is connected with the other end. Also, one end of a coil L2 connected with the coil L1 by mutual inductance is grounded, and the other end is connected through a diode DR with a connection between the power source Vcc and the coil L1. Then, a positive driving signal is impressed to the base of a transistor TR1 so that the transistor TR1 can be turned on, and currents are supplied from the power source Vcc so that the coil L1 can be driven. When the transistor TR1 is turned off, energy induced to the coil 2 by energy remaining in the coil L1 is allowed to regress through the diode DR to the power source.