To provide an atmosphere heat treatment furnace capable of restraining adhesion of tar in an exhaust gas flow passage.

The atmosphere heat treating furnace 1 is provided with a furnace body 2 having a heat treatment chamber 22; and at least one combustion case 3D arranged to heat-exchange to the heat treatment chamber 22, and having a combustion chamber 31D, a furnace inner side communication port 32 D communicating the combustion chamber 31D with the heat treatment chamber 22, a furnace outer side communication port 33D communicating the combustion chamber 31D with the outside of the furnace, and an oxygen supply port 34D arranged between the furnace inner side communication port 32D and the furnace outer side communication port 33D and supplying oxygen to the combustion chamber 31D. During heating, exhaust gas of the heat treatment chamber 22 flows into the combustion chamber 31D through the furnace inner side communication port 32D, is mixed with oxygen supplied through the oxygen supply port 34D, is burned by transferred heat from the heat treatment chamber 22, and flows out of the furnace through the furnace outer side communication port 33D.

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