An inverter device is formed of the two systems of inverters stored inside a cylindrical metal casing. Each inverter converts DC power to three-phase AC power. The inverters are formed of power semiconductor elements, DC bus bars through which DC power supplied to the respective power semiconductor elements, capacitors connected to the DC bus bars, and switches connected between the respective DC bus bars and the DC input terminals. High-impedance switches are disposed in the vicinity of the DC input terminals. Hence, electromagnetic noises generated by switching actions of the power semiconductor elements are circulated within the inverters by way of the capacitors and eventually attenuated.