PURPOSE: To reproduce a previous dim mode when electric power is applied, and prevent malfunction due to static electricity.

CONSTITUTION: A plural dim modes are selected by operation of switches 41, 42, 43. Result of selection of the switches is given to an input IN of a changing circuit 27 by photocouplers P14, P15, P16. Power of the changing circuit 27 is rectified, stabilized by a three-terminal regulator 26, and supplied from a DC power line 28 through a diode 29. A capacitor 50 is connected between power supply terminals of the changing circuit 27. When power from a commercial power supply 21 is not supplied, charges accumulated in the capacitor 50 are supplied for a working current for the changing circuit 27. When the power is supplied from the commercial power supply 21, the changing circuit 27 can operate in the dim mode held by the working current from the capacitor 50.