To accomplish the elongation of life of a heat insulating layer, by suppressing the compression of a heat insulating material such as ceramic fiber or the like caused by the thermal expansion of an inverted cup in a heat insulating layer, and lessening the deformation due to the friction between the inverted cup standing and the heat insulating material as far as possible.

This device is equipped with a high-pressure container 1, covers 2 and 3, a heat insulating layer 4, a heater 5, and a hearth 7, and the heat insulating layer 4 is constituted by superposing at least two pieces of inverted cups 11 and 12 different in diameter from each other on top of the other so as to form spaces, and filling at least one of the spaces between the adjacent inverted cup 11 and 12 with ceramic fibers 21 or heat insulating material having the same heat insulating property as this. In this case, at least one inverted inside cup 11 corresponding to the space filled with the heat insulating material 21 is constituted of material smaller in thermal expansion coefficient than the outer inverted cup 12. Moreover, it is also constituted of a material where the thermal expansion coefficient is small and the quantity of thermal expansion in the elevated temperature range at hot isotropic pressurizing operation becomes small.