PURPOSE: To control temp. in a furnace in a wide range according to the necessity of a material to be heated even if radiant tube burners are used for the burning of the fixed quantity of gas according to the demand of protective gas, in an atmospheric heat treatment furnace using non-oxidized atmospheric gas discharged from the radiant tube burners in a heating chamber as the protective gas.

CONSTITUTION: The radiant tube burners 11 burning rich fuel are disposed in a heating chamber 1 and used for the burning of the fixed quantity of gas and the non-oxidized atmospheric gas discharged from the radiant tube burners 11 is used for the protective gas. Further, the cooling means 16 of the atmospheric gas in the heating chamber 1 is disposed, and by adjusting the cooling degree of the cooling means 16, the temp. in the furnace is controlled.