A vertical heat treating furnace comprising: an outer body having an exterior wall and an interior well, thereby forming a first receiving space, and having a first side and a second side opposite to said first side, wherein said first side being provided with an opening of said first receiving space, and said second side is a sealed side; an inner body being spaced and fixed in said first receiving space of said outer body, said inner body having an outer wall and an inner wall, thereby forming a second receiving space, having a third side and a fourth side opposite to said third side, a part of said third side being connected with said first side by a lower sealed side thereby forming an opening of said second receiving space, and said fourth side is a sealed side, wherein a gas circulation chamber being formed between said outer wall of said inner body and said interior wall of said outer body, and a reaction chamber being formed inside said inner wall of said inner body; a gate door having an outer surface and an inner surface, being contacted with said opening of said second receiving space of said third side by said inner surface, thereby either of said gas circulation chamber and said reaction chamber being an independent chamber; a gas supplying mechanism constituted by a plurality of gas pipes, said plurality of gas pipes passing through said outer surface and said inner surface of said gate door and being adapted to introduce gases into said gas circulation chamber and said reaction chamber via said opening of said second receiving space and said lower sealed side; and characterized by a controller being set outside said outer body for controlling a gas supplying mechanism adapted to control a supply amount of a first gas and a second gas into said gas circulation chamber and said reaction chamber in a way to form a first pressure (P 1) in said gas circulation chamber and to form a second pressure (P 2) in said reaction chamber, wherein the first pressure (P 1) is greater than the second pressure (P 2). an outer body having an exterior wall and an interior well, thereby forming a first receiving space, and having a first side and a second side opposite to said first side, wherein said first side being provided with an opening of said first receiving space, and said second side is a sealed side; an inner body being spaced and fixed in said first receiving space of said outer body, said inner body having an outer wall and an inner wall, thereby forming a second receiving space, having a third side and a fourth side opposite to said third side, a part of said third side being connected with said first side by a lower sealed side thereby forming an opening of said second receiving space, and said fourth side is a sealed side, wherein a gas circulation chamber being formed between said outer wall of said inner body and said interior wall of said outer body, and a reaction chamber being formed inside said inner wall of said inner body; a gate door having an outer surface and an inner surface, being contacted with said opening of said second receiving space of said third side by said inner surface, thereby either of said gas circulation chamber and said reaction chamber being an independent chamber; a gas supplying mechanism constituted by a plurality of gas pipes, said plurality of gas pipes passing through said outer surface and said inner surface of said gate door and being adapted to introduce gases into said gas circulation chamber and said reaction chamber via said opening of said second receiving space and said lower sealed side; and characterized by a controller being set outside said outer body for controlling a gas supplying mechanism adapted to control a supply amount of a first gas and a second gas into said gas circulation chamber and said reaction chamber in a way to form a first pressure (P 1) in said gas circulation chamber and to form a second pressure (P 2) in said reaction chamber, wherein the first pressure (P 1) is greater than the second pressure (P 2).