To surely discharge the electric charge of a smoothing capacitor of an inverter device at the tame of maintenance.

An inverter device has a converter section 1 to convert AC to DC, a smoothing capacitor 3, an inverter section 2 to reversely convert DC to AC of variable voltage and variable frequency, and a resistor for braking 4. In this inverter device, a relay 20 is installed which has a normally-closed contact 20a to selectively allow the resistor for braking 4 to conduct and the cutoff of an input power supply is detected by a power supply cutoff detecting section 22. When the input power supply is cut off, the conduction of the relay 20 is stopped by means of a relay driving section 23 and then the normally- closed contact 20a is closed.