A method of lubrication of a buffering device, with an internal cylinder, an external cylinder, a plug, arranged at an end of the internal cylinder and a piston with a piston head, of an operating mechanism of a switchgear, comprising: arranging a lubricating plug at an end of the internal cylinder of the buffering device, having a flow path in an interior of said lubricating plug, said lubricating plug being connected with a conduit; fixing a packing in a vicinity of a tip of said lubricating plug; bifurcating said conduit into two branches; connecting one of said conduits with a vacuum pump; connecting another of said conduits with a container that accumulates said operating fluid; arranging a first valve on a vacuum pump side of said conduit; arranging a second valve on a container side of said conduit; closing said second valve and opening said first valve, and putting the interior of said buffering device into a vacuum condition by said vacuum pump, and then introducing said operating fluid into an interior of said buffering device; wherein lubrication of said interior of said buffering device with said operating fluid within said container is effected by closing said first valve and opening said second valve, characterized by the steps of: forming said lubricating plug with cutaway sections at its own tip; wherein said lubricating plug is inserted while forcing the plug of the buffering device into the interior of said internal cylinder; inserting a plate between the piston head of the buffering device and the external cylinder of the buffering device in order to compensate for an amount of change of volume resulting from insertion of said lubricating plug into an interior of said internal cylinder of the buffering device; and introducing said operating fluid into an interior of said buffering device after expansion of a space where said operating fluid in said buffering device enters. arranging a lubricating plug at an end of the internal cylinder of the buffering device, having a flow path in an interior of said lubricating plug, said lubricating plug being connected with a conduit; fixing a packing in a vicinity of a tip of said lubricating plug; bifurcating said conduit into two branches; connecting one of said conduits with a vacuum pump; connecting another of said conduits with a container that accumulates said operating fluid; arranging a first valve on a vacuum pump side of said conduit; arranging a second valve on a container side of said conduit; closing said second valve and opening said first valve, and putting the interior of said buffering device into a vacuum condition by said vacuum pump, and then introducing said operating fluid into an interior of said buffering device; wherein lubrication of said interior of said buffering device with said operating fluid within said container is effected by closing said first valve and opening said second valve, characterized by the steps of: forming said lubricating plug with cutaway sections at its own tip; wherein said lubricating plug is inserted while forcing the plug of the buffering device into the interior of said internal cylinder; inserting a plate between the piston head of the buffering device and the external cylinder of the buffering device in order to compensate for an amount of change of volume resulting from insertion of said lubricating plug into an interior of said internal cylinder of the buffering device; and introducing said operating fluid into an interior of said buffering device after expansion of a space where said operating fluid in said buffering device enters. forming said lubricating plug with cutaway sections at its own tip; wherein said lubricating plug is inserted while forcing the plug of the buffering device into the interior of said internal cylinder; inserting a plate between the piston head of the buffering device and the external cylinder of the buffering device in order to compensate for an amount of change of volume resulting from insertion of said lubricating plug into an interior of said internal cylinder of the buffering device; and introducing said operating fluid into an interior of said buffering device after expansion of a space where said operating fluid in said buffering device enters.