PURPOSE: To make it possible to arrange a conservator at a desired location by such an arrangement wherein a pressurizing device the pressurizing force thereof is adjustable is provided in the conservator and the device is designed so that it is capable of pressurizing air insulated from insulation oil in the conservator by an insulation diaphragm in the direction of the side of insulation oil.

CONSTITUTION: In a conservator 20, insulation oil 23 is insulated from air 24 by an insulation membrane 22 such as a bellows, diaphragm, etc. The membrane 22 is equipped with a pressurizing device 25 of which pressurizing force is adjustable and which is composed so that it is capable of pressurizing the membrane in the direction of oil 23. A pressurizing force which is the same or slightly higher than the value of maximum oil level acts on the surface of oil under the membrane 22 and the function of a conservator is satisfied by said mechanism. Consequently, the conservator can be installed at a desired location, e.g. on the floor.