PURPOSE: To facilitate maintenance and inspection of a thermal insulating layer an fully utilize the inner volume of a high pressure container by a method wherein there is provided an ascending or descending means for inputting or outputting a processed item through insertion or removal of a lower lid and for inputting or outputting a thermal insulating layer to a high pressure chamber as the lower lid is inserted or removed.

CONSTITUTION: A high pressure chamber 3 is defined by covering an upper lid 2A and a lower lid 2B on each of openings 1A, 1B in a high pressure cylinder 1 having an upper opening 1A and a lower opening 1B, and then a heat insulating layer 7 forming a furnace chamber 6 provided with a heater 5 inside of it is arranged in the high pressure chamber 3. A processed item 12 inserted into a furnace chamber 6 is pressurized under a hot uniform pressure. In such a hot uniform pressurizing device as described above, an electrical power supplying means 10 for a heater 5 is removably arranged at the lower lid 2B and further there is provided a supporting means 8 for removably supporting the thermal insulating layer 7 under an external operation against the upper lid 2A. Under an operation of the ascending or descending means 9, the processed item 12 is inputted or outputted under an insertion or a removal of the lower lid 2B and at the same time the thermal insulating layer 7 having the supporting means 8 released is ascended or descended.