Abstract: A method for circulating a gas in an autoclave which comprises a pressure container (A) having a wind tunnel (7) in which moldable materials (1) are placed and the gas is circulated by a blow fan (33), the pressure container (A) being sealably closed by a door, the layers of each of the materials (1) are compressed, heated, adhered together, and set in the pressure container (A) producing swirling of the gas coming out of an outer duct formed between the inner face Aa of the pressure container (A) and the wind tunnel (7) by guide blades (H), diverting the gas at the inner face (2a) of the door (2), and directing the diverted gas to flow through the inside (7b) of the wind tunnel (7) with the swirl. The apparatus for circulating gas has guide blades (H) for swirling the gas going out of the outer duct (7a) provided in the outer duct, whereby the gas is diverted at the inner face (2a) of the door (2), and is directed to flow through the inside (7b) of the wind tunnel (7) with the swirl.