To shorten an in-furnace cooling time after HIP treatment without damaging an effective volume rate.

A reversed cup-shaped insulating layer 5 is provided inside a high pressure vessel 2, thereby surrounding a furnace compartment 6. This device is designed to treat an article 8 based on HIP treatment in the aforesaid furnace compartment 6 surrounded with the insulating layer. Gas distribution holes 15 and 16, which communicate the inside and the outside of the furnace compartment 6, are provided in the upper part and the lower part of an inner casing 11 in the insulation layer 5 where a second valve means is provided so as to open and close freely at least one of the distribution holes 15 and 16.