PURPOSE: To make it possible to perform automatic detection of the fault of wire breakdown, by superimposing a DC signal on a detecting coil which outputs an AC signal corresponding to the vibration, and issuing a report and the like based on the change in the DC signal.

CONSTITUTION: The AC signal corresponding to the vibration is generated from the detecting coil 11 of a vibration sensor 1, which is mounted on a body to be measured and vibrated as a unitary body. The signal is applied to a signal processor 3 from one terminal 13 of the coil 11 through a signal line 12. Meanwhile, the DC current flows from a DC constant voltage power source 29 to a resistor 21, the coil 11, the other output terminal 14 of the coil 11, a resistor 22, and the like. Since the DC resistance of the coil 11 is small, the DC voltage, which is superimposed on the AC signal at the output terminal 14, becomes a constant value corresponding to a voltage dividing ratio of the resistors 21 and 23. The AC signal is moved by an LPF formed by a capacitor 26 and the resistor 23. The constant DC voltage is applied to a comparator 25 through a capacitor 24. When the signal line 12 or the coil 11 is broken by the vibration, the output of the comparator 25 is inverted. The reporting, controlling, and the like are performed based on said output, and the fault of the wire breakdown can be automatically detected.