An LED driver circuit that is adapted to control driving of an LED lamp in response to an on/off state of a mechanical switch device, comprising: a first terminal connectable to a current path of the switch device at one end thereof; a second terminal connectable to the current path of the switch device at another end thereof; a detection circuit that is adapted to periodically detect a current flowing to the first terminal and output a detection signal responsive to a result of the detection at a first node; a comparison circuit that is adapted to compare a detection voltage responsive to the detection signal with a threshold voltage and output a comparison result signal responsive to a result of the comparison; and a control circuit that is adapted to control a current detection operation of the detection circuit and control driving of the LED lamp based on the comparison result signal, wherein the control circuit is adapted to determine that the switch device is in an on state and the current path is conductive between the one end and the other end if the comparison result signal indicates that the detection voltage is equal to or higher than the threshold voltage, and is adapted to determine that the switch device is in an off state if the comparison result signal indicates that the detection voltage is lower than the threshold voltage, wherein the detection circuit comprises: a first switch element that is connected to the first terminal at one end thereof and is adapted to be turned on and off under the control of the control circuit; a detection capacitor that is connected to another end of the first switch element at one end thereof and to the first node at another end thereof; a detection resistor that is connected to the first node at one end thereof and to the second terminal at another end thereof; and a discharge resistor that is connected or switchable in parallel with the detection resistor and the detection capacitor between the other end of the first switch element and the second terminal, the discharge resistor being connected or switchable to the other end of the first switch element at one end thereof and to the second terminal at another end thereof, wherein the control circuit is adapted to control the first switch element to periodically switch on and off, and the detection circuit is adapted to output the detection signal at the first node. a first terminal connectable to a current path of the switch device at one end thereof; a second terminal connectable to the current path of the switch device at another end thereof; a detection circuit that is adapted to periodically detect a current flowing to the first terminal and output a detection signal responsive to a result of the detection at a first node; a comparison circuit that is adapted to compare a detection voltage responsive to the detection signal with a threshold voltage and output a comparison result signal responsive to a result of the comparison; and a control circuit that is adapted to control a current detection operation of the detection circuit and control driving of the LED lamp based on the comparison result signal, wherein the control circuit is adapted to determine that the switch device is in an on state and the current path is conductive between the one end and the other end if the comparison result signal indicates that the detection voltage is equal to or higher than the threshold voltage, and is adapted to determine that the switch device is in an off state if the comparison result signal indicates that the detection voltage is lower than the threshold voltage, wherein the detection circuit comprises: a first switch element that is connected to the first terminal at one end thereof and is adapted to be turned on and off under the control of the control circuit; a detection capacitor that is connected to another end of the first switch element at one end thereof and to the first node at another end thereof; a detection resistor that is connected to the first node at one end thereof and to the second terminal at another end thereof; and a discharge resistor that is connected or switchable in parallel with the detection resistor and the detection capacitor between the other end of the first switch element and the second terminal, the discharge resistor being connected or switchable to the other end of the first switch element at one end thereof and to the second terminal at another end thereof, wherein the control circuit is adapted to control the first switch element to periodically switch on and off, and the detection circuit is adapted to output the detection signal at the first node. a first switch element that is connected to the first terminal at one end thereof and is adapted to be turned on and off under the control of the control circuit; a detection capacitor that is connected to another end of the first switch element at one end thereof and to the first node at another end thereof; a detection resistor that is connected to the first node at one end thereof and to the second terminal at another end thereof; and a discharge resistor that is connected or switchable in parallel with the detection resistor and the detection capacitor between the other end of the first switch element and the second terminal, the discharge resistor being connected or switchable to the other end of the first switch element at one end thereof and to the second terminal at another end thereof, wherein the control circuit is adapted to control the first switch element to periodically switch on and off, and the detection circuit is adapted to output the detection signal at the first node.