PURPOSE: To effectively control an exciting current and to easily release this control function.

CONSTITUTION: A bias resistor 274 is connected between an L terminal and an IG terminal of a voltage controller 2. The resistor 274 biases an L terminal voltage substantially to a battery voltage at the time of cutting OFF a transistor 281. The L terminal voltage becomes a voltage between a collector and an emitter of the transistor 281 at the time of driving a charge lamp 5. An exciting current limiter 25 turns on a transistor 254 when the exciting current is a predetermined value or more, thereby holding an output transistor 24 in a cut-off state. An inhibiting circuit 27 turns on a transistor 273 when the L terminal voltage is Ve or lower which is lower than the voltage between the collector and the emitter of the transistor 281, thereby cutting OFF the transistor 254 of the limiter 25.