An LED lamp lighting device that is connected between a first power supply terminal on a low potential side of a lamp driving power supply and a second power supply terminal on a high potential side of the lamp driving power supply, receives a driving current from the lamp driving power supply, and causes the driving current to illuminate a first lamp circuit and a second lamp circuit connected in series, the LED lamp lighting device comprising: a first terminal connected to the first power supply terminal; a second terminal connected to the second power supply terminal; said first lamp circuit including one LED lamp or a plurality of series connected LED lamps (LH1, LH2), with a first end connected to the first terminal; and said second lamp circuit including one LED lamp or a plurality of series connected LED lamps (LL1, LL2), with a first end connected to a second end of the first lamp circuit and a second end connected to the second terminal; characterized by a switch circuit comprising a reference node connected to the second end of the first lamp circuit and said switch circuit is operable to electrically connect said reference node between a first contact and and a second contact; a control switch element with a first end connected to the first terminal and a second end connected to the first contact or the first end connected to the second contact and the second end connected to the second terminal; and a switch control circuit that controls the control switch element according to a potential difference between the first end and the second end of the control switch element, wherein the switch control circuit turns on the control switch element if the potential difference between the first end and the second end of the control switch element is at least a predetermined reference voltage, and the switch control circuit turns off the control switch element if the potential difference between the first end and the second end of the control switch element is smaller than the reference voltage. a first terminal connected to the first power supply terminal; a second terminal connected to the second power supply terminal; said first lamp circuit including one LED lamp or a plurality of series connected LED lamps (LH1, LH2), with a first end connected to the first terminal; and said second lamp circuit including one LED lamp or a plurality of series connected LED lamps (LL1, LL2), with a first end connected to a second end of the first lamp circuit and a second end connected to the second terminal; characterized by a switch circuit comprising a reference node connected to the second end of the first lamp circuit and said switch circuit is operable to electrically connect said reference node between a first contact and and a second contact; a control switch element with a first end connected to the first terminal and a second end connected to the first contact or the first end connected to the second contact and the second end connected to the second terminal; and a switch control circuit that controls the control switch element according to a potential difference between the first end and the second end of the control switch element, wherein the switch control circuit turns on the control switch element if the potential difference between the first end and the second end of the control switch element is at least a predetermined reference voltage, and the switch control circuit turns off the control switch element if the potential difference between the first end and the second end of the control switch element is smaller than the reference voltage.