Applicant has disclosed a method and apparatus for a bipolar automotive electrical system. According to a length of an original, a flapper is switched to a position to guide the original to one of the first switchback path and the second switchback path. In addition, a control circuit 8 is structured to control a power supply 26 or onoff of the lamp 2, based on a measurement results of a temperature detecting devices 30 and 32, where the temperature detecting device 30 measures a temperature in the vicinity of the liquid crystal valve section 4 and the temperature detecting device 32 measures an external temperature of a body. A guide member extends from the underside of the casing.