To provide an exhaust structure of a heating furnace, in which a negative pressure is prevented from being generated in a chamber in which the furnace is installed, and the heating loss is less.

A sintering furnace is installed in a chamber 22, and an exhaust duct 24 discharges exhaust gas of the sintering furnace to the outside 23. The exhaust duct 24 penetrates a through hole 26 made in a roof 25. An outer casing 27 is provided to the through hole 26, and the duct 24 is passed through the casing 27, and then an opening 28 is made between them for letting in the outside air. The exhaust gas of the furnace is discharged to the outside through the duct 24. A negative pressure is caused in the chamber 22 due to the discharge of the exhaust gas, and outside air is drawn from the opening 28 into the chamber 22 to cause the negative pressure to disappear. The outside air is heated by heat exchanging with the exhaust duct 24 while passing through the opening 28.