A gas-insulated electric device, by which a cross-sectional area of a central conductor can be reduced. The gas-insulated electric device includes an insulation tube that ranges to portions facing to ground potential portions for a central conductor and to upper-lower portions along the grounding potential portions, and is coaxially arranged along the central conductor in a state where a gap intervenes between the central conductor and the insulation tube; a conductive layer that is formed on an inner surface of an insulation tube and is electrically connected to the central conductor; and a ground layer that is formed on an inner surface or an outer surface of the insulation tube and is grounded; in which heat generated from the central conductor is radiated by convecting the insulation gas through the gap between the central conductor and insulation tube.