PURPOSE: To use both a battery pack and an AC adaptor and to prevent the service life of a halogen lamp from being decreased when the AC adaptor is in use.

CONSTITUTION: A changeover lever 100 is provided freely retractively to a back side 33 and a slide switch 102 connects to the changeover lever 100. A bypass resistor 103 is connected to the slide switch 102. When an AC adaptor P is connected, the changeover lever 100 is pushed into the inside by a mount face P1 of the AC adaptor P to open the slide switch 102. Thus, an input current is supplied through the resistor 103 and an input voltage is dropped. Thus, even when the AC adaptor P is in use, a high voltage is not applied to a halogen lamp 71, the shortage in the service life of the halogen lamp 71 is prevented.