A gas insulated electrical equipment comprising: a high-voltage conductor to be electrically charged; a hermetically sealed container to be filled with insulating gas; one or more insulating spacers (11, 11a, 11b) for dividing the hermetically sealed container into a plurality of gas compartments (111, 112) and supporting the high-voltage conductor, keeping insulation between the high-voltage conductor and the hermetically sealed container; and a pressure release device (2, 2a, 2b) equipped with a mouth of flow channel adapted to allow the inside and the outside of the hermetically sealed container to communicate with each other so as to hermetically seal the hermetically sealed container by closing the mouth of flow channel and release the pressure in the hermetically sealed container by opening the mouth of flow channel, wherein provided that the minimum flow channel cross-sectional area that is the area of the cross section that is perpendicular to the flow direction of the insulating gas in the mouth of flow channel is SD, the working pressure at which the pressure release device (2, 2a, 2b) starts operating is Pop, and with regard to the arc that occurs in the inside of the hermetically sealed container, the average effective value of the arc current that is an estimation value is Ia and the arc ignition time that is also an estimation value is Ta, while the volume of the gas compartment that can be a target of occurrence of the arc is VT and the withstanding pressure of the insulating spacer (11, 11a, 11b) is PD and the constant indicating the efficiency of arc energy that contributes to the rise of pressure is α, the first constant and the second constant that respectively define the pressure rising characteristics of the insulating gas and the pressure release characteristics of the insulating gas being Kga and Kgb and that the equation of Kc = Kga × Ia α / VT is made to hold true; SD is found within the range satisfying the requirements of conditional formula of SD > VT / Kgb × log Kc × Ta − Pop / Kc × Ta − PD; and the pressure release device (2, 2a, 2b) is so designed as to hermetically seal the hermetically sealed container and maintain the hermetically sealed state in an ordinary condition where the pressure in the gas compartment that can be a target of occurrence of the arc does not exceed the working pressure (Pop) but release the pressure in the hermetically sealed container in an abnormal condition where the pressure in the gas compartment that can be a target of occurrence of the arc exceeds the working pressure (Pop). a high-voltage conductor to be electrically charged; a hermetically sealed container to be filled with insulating gas; one or more insulating spacers (11, 11a, 11b) for dividing the hermetically sealed container into a plurality of gas compartments (111, 112) and supporting the high-voltage conductor, keeping insulation between the high-voltage conductor and the hermetically sealed container; and a pressure release device (2, 2a, 2b) equipped with a mouth of flow channel adapted to allow the inside and the outside of the hermetically sealed container to communicate with each other so as to hermetically seal the hermetically sealed container by closing the mouth of flow channel and release the pressure in the hermetically sealed container by opening the mouth of flow channel, wherein provided that the minimum flow channel cross-sectional area that is the area of the cross section that is perpendicular to the flow direction of the insulating gas in the mouth of flow channel is SD, the working pressure at which the pressure release device (2, 2a, 2b) starts operating is Pop, and with regard to the arc that occurs in the inside of the hermetically sealed container, the average effective value of the arc current that is an estimation value is Ia and the arc ignition time that is also an estimation value is Ta, while the volume of the gas compartment that can be a target of occurrence of the arc is VT and the withstanding pressure of the insulating spacer (11, 11a, 11b) is PD and the constant indicating the efficiency of arc energy that contributes to the rise of pressure is α, the first constant and the second constant that respectively define the pressure rising characteristics of the insulating gas and the pressure release characteristics of the insulating gas being Kga and Kgb and that the equation of Kc = Kga × Ia α / VT is made to hold true; SD is found within the range satisfying the requirements of conditional formula of SD > VT / Kgb × log Kc × Ta − Pop / Kc × Ta − PD; and the pressure release device (2, 2a, 2b) is so designed as to hermetically seal the hermetically sealed container and maintain the hermetically sealed state in an ordinary condition where the pressure in the gas compartment that can be a target of occurrence of the arc does not exceed the working pressure (Pop) but release the pressure in the hermetically sealed container in an abnormal condition where the pressure in the gas compartment that can be a target of occurrence of the arc exceeds the working pressure (Pop).