An apparatus for sensing input power source includes; an input power source; a rectifier for rectifying input power source (Vin) of the input power source into rectified power source (Vr); a dimming interface for sensing the state of the input power source; a first light; and a converter for converting the rectified power source (Vr) into a first power source (V21) and a second power source (V22) which were preset to apply them to the dimming interface and the first light, wherein the dimming interface and the first light are connected with the converter in a feedback type.