Abstract: An apparatus for detecting, for example, the disconnection of signal lights such as flashers for vehicles and for warning of this disconnection has a detecting resistor element for converting an ON current of the signal lights into a voltage signal. The voltage signal detected by this resistor element is compared with a reference voltage which is set at a discrimination/oscillation control circuit so as to detect if the detecting voltage signal is lower than the reference voltage. When such a state is detected, the oscillation frequency of an oscillator for changing the flashing frequency of the signal light is doubled. The disconnection of the lights can be detected by observing the frequency of the flashing signal. The detecting resistor element consists of a resistive wiring formed of a resistive material which is processed so as to have a smaller resistance than desired.