To improve the boosting ability of a transformer by sufficiently bringing out the performance of the transformer.

A battery terminal 32 and a transistor 34 are connected in series with the primary coil 33a of a transformer 33 and, at the same time, a capacitor 36 is connected to the secondary coil 33b. A microcomputer 4 turns on the transistor 34 by outputting a charge signal to the transistor 34. When the transistor 34 is turned on, a current detecting circuit 40 detects the primary current flowing to the primary coil 33a and, when the primary current is made to become a set value by means of a comparator 42, an OR gate 43, a flip flop 44, and an AND gate 45, turns off the transistor 34. In addition, the microcomputer 4 detects the voltage of a battery and, when the voltage is low, lowers the charging frequency of the transistor 34.