According to one embodiment, a dynamo-electric machine includes a rotor, a stator, a frame, a shaft sealing device, and a gas purity maintainer. The gas purity maintainer includes an expansion tank, a first mist collecting section, a valve unit, a drain pot, and an instrument panel. The first mist collecting section is provided in the middle of a scavenging pipe extending from the expansion tank to discharge a coolant gas from the expansion tank. A downstream in the first mist collecting section is higher than an upstream.