To provide a method of detecting disconnection in an electric wire applicable to the electric wire under use, and capable of detecting surely the disconnection.

A pulse signal is impressed to the electric wire 8 to measure a current flowing in the electric wire 8 therein, a current waveform thereof is compared with a current waveform for reference, and the disconnection is detected based on a waveform difference. This method is thereby applicable also for the electric wire 8 under the use electrified with electric power or a signal, and the disconnection is surely detected.