A converter having an inductor, a first switch, a second switch, a third switch, and a fourth switch connected between the other ends of the inductor and the second switch. The converter is adapted to turn ON/OFF individually the first switch, the second switch, the third switch and the fourth switch so as to convert a voltage applied between the other ends of the first switch and the second switch. Also included is a diode, a maintaining device and a release device. The generating device generates small/large output electric current in correspondence with high/low of a voltage of a connection node between the semiconductor transistor and the resistor, and increases the output electric current by switching a voltage applied on the third end from a first voltage to a second voltage lower than the first voltage.