Gas-insulated electric equipment with earthing switch

A gas-insulated electric equipment such as a gas-insulated switch gear or gas insulated substation equipment, and more specifically an improvement in an earthing switch (500) built in a gas-insulated electric equipment. The earthing switch is provided with insulated guiding devices (52, 53, 54) which function selectively to electrically connect the electric contacts (211, 212) in the earthing switch (500) to an external device outside of the enclosure (501, 502) thereof in an isolated relation of the contacts from the enclosure while the enclosure is maintained gas-tight therein. When the earthing switch is turned on, that is, when the electric contact (511, 512) in the earthing switch is brought into contact with a mating contact (211, 212) on a conductor (201, 202), an insulation testing device provided with a test voltage source (70) can be connected to an end portion (541) of said insulated guiding device (52, 53, 54) outside of the enclosure. In this way, the conductor associated with the contact is tested with respect to its insulation.