PURPOSE: To obtain the monitoring device for an electric equipment with high reliability for confirming the operation of a voltage sensor.

CONSTITUTION: A changeover switch 2 to turn on/off a power source, a fixed voltage power unit 3 to transform an input voltage and a voltage sensor 4 to output an alarm output signal in the case of lowering the output voltage of the fixed voltage power unit are connected to a power supply input terminal stand 1. A power supply terminal 5 of the voltage sensor 4 is connected so as to be taken from the primary side of the changeover switch 2. When the changeover switch 2 is turned off, a power source 5 for the voltage sensor is still turned on but the input power supply of the fixed voltage power unit 3 is cut off and there is not output from the fixed voltage power unit. As the result, since the alarm output signal is outputted when the voltage sensor 4 can normally detect the output reduction of the fixed voltage power unit 3, the operation of the voltage sensor can be confirmed.