Monitoring device of the open or closed state of an electric line of a railway vehicle, and electric line of a railway vehicle

A monitoring device of the open or closed state of an electric line is disclosed. The device includes a first connection terminal and a second terminal connected to the electric line, a current generator that provides a non-zero reference current when there is a voltage greater than a predetermined minimum voltage Vmin at its ends and provides a zero current when there is a voltage less than the predetermined minimum voltage Vmin at its ends, at least one opto-isolator means including a lighting device and a respective photosensitive semi-conductor element, and a current detection and power supply module that detects current flowing therein, supplies a supply current to the lighting device when the detected current is equal to or greater than the reference current, and supplies a zero supply current to the lighting device when the detected current is less than the reference current.