PURPOSE: To make the quality of an article const. and to shorten the heat treating time by a method wherein the temp. distribution in a room under high temp. and high pressure storing the article to be treated is made const. and, thereafter, while the room is made vacuum, the article is heated by using a heating means arranged to be close to the article.

CONSTITUTION: A highly precise article 24 is arranged in a room 26 and heating means 28, 30, 31 and 44 provided on the periphery of the room 26 are actuated and, at the same time, inner pressure in the room is elevated. After the room temp. reaches a specified temp., while this temp. is kept at a const. temp. and the pressure in the room is kept at a high pressure atmosphere, a required heat treatment is performed while the article is kept at const. pressure and temp. After a specified time passes through, while the room temp. is kept const., the pressure in the room is decreased down to at most atmospheric pressure to perform degassing treatment. Then, the pressure in the room is elevated up to at least atmospheric pressure and while the room temp. is gradually lowered, aging treatment of the article 24 is performed. While the inside of the room is kept under a furthermore elevated pressure condition, the heating means is not actuated to quench the article 24 and the pressure in the room is decreased to atmospheric pressure and the article 24 is taken out.