A vehicle LED lighting device system comprising: an LED lighting device having an LED light source, a substrate on which the LED light source is mounted, a housing equipped with the substrate, and a lens covering the LED light source and which is attached to the housing; an operation switch configured to turn on and turn off the LED light source; a power supply connected to an input side of the operation switch; a plus cable that connects an output side of the operation switch and the LED lighting device, the plus cable being configured to supply an electric current from the power supply to the LED light source; and a minus cable configured to return an electric current that flows through the LED light source to a side of the power supply; the vehicle LED lighting device system further comprising: a switching element disposed in series with the LED light source and configured to interrupt an electric current that flows to the LED light source; and a detector configured to detect a voltage on the output side of the operation switch and cause the switching element to interrupt the electric current; characterised in that the switching element and the detector are disposed in an interior of the LED lighting device, and in that the detector includes a leakage detecting resistance, a resistance, and a Zener diode, wherein the resistance and the Zener diode (Z1,Z2), which are connected in series, are connected in parallel with the leakage detecting resistance, such that an electric current flowing through the resistance and the Zener diode (Z1,Z2) is smaller than an electric current flowing through the leakage detecting resistance, and in a case that a voltage across the leakage detecting resistance is less than or equal to a value predetermined by the Zener diode (Z1, Z2), the detector causes the switching element to interrupt the electric current. an LED lighting device having an LED light source, a substrate on which the LED light source is mounted, a housing equipped with the substrate, and a lens covering the LED light source and which is attached to the housing; an operation switch configured to turn on and turn off the LED light source; a power supply connected to an input side of the operation switch; a plus cable that connects an output side of the operation switch and the LED lighting device, the plus cable being configured to supply an electric current from the power supply to the LED light source; and a minus cable configured to return an electric current that flows through the LED light source to a side of the power supply; the vehicle LED lighting device system further comprising: a switching element disposed in series with the LED light source and configured to interrupt an electric current that flows to the LED light source; and a detector configured to detect a voltage on the output side of the operation switch and cause the switching element to interrupt the electric current; characterised in that the switching element and the detector are disposed in an interior of the LED lighting device, and in that the detector includes a leakage detecting resistance, a resistance, and a Zener diode, wherein the resistance and the Zener diode (Z1,Z2), which are connected in series, are connected in parallel with the leakage detecting resistance, such that an electric current flowing through the resistance and the Zener diode (Z1,Z2) is smaller than an electric current flowing through the leakage detecting resistance, and in a case that a voltage across the leakage detecting resistance is less than or equal to a value predetermined by the Zener diode (Z1, Z2), the detector causes the switching element to interrupt the electric current. a switching element disposed in series with the LED light source and configured to interrupt an electric current that flows to the LED light source; and a detector configured to detect a voltage on the output side of the operation switch and cause the switching element to interrupt the electric current; characterised in that the switching element and the detector are disposed in an interior of the LED lighting device, and in that the detector includes a leakage detecting resistance, a resistance, and a Zener diode, wherein the resistance and the Zener diode (Z1,Z2), which are connected in series, are connected in parallel with the leakage detecting resistance, such that an electric current flowing through the resistance and the Zener diode (Z1,Z2) is smaller than an electric current flowing through the leakage detecting resistance, and in a case that a voltage across the leakage detecting resistance is less than or equal to a value predetermined by the Zener diode (Z1, Z2), the detector causes the switching element to interrupt the electric current.