Abstract: A city bus line enquiry machine includes a diode selector circuit, which includes a plurality of key switches marked with respective names of bus stops and a plurality of light emitting diodes marked with respective bus line codes and connected to the key switches respectively, and a power supply and sound generating circuit, which provides the necessary working voltage to the automatic lighting device and gives sound when either key switch of the diode selector circuit is depressed, wherein when either key switch bearing the name of a respective bus stop is depressed, the related light emitting diodes are turned on to show available bus lines passing through the bus stop in question.