PURPOSE: To obtain high quality atmospheric gas extremely low in the concn. of unburnt hydrocarbon and residual oxygen without generating soot, by the catalytic action of the oxidizing catalyst of a surface combustion burner.

CONSTITUTION: A surface combustion burner 3, wherein an oxidizing catalyst is supported by a heat resistant porous body part 4, is provided in a combustion furnace 1 to burn a gaseous mixture of fuel and air and the heat generated in the furnace is removed by the heat exchanger 8 provided to the furnace. The exhaust gas of the furnace 1 is cooled and dehumidified by a copper 10 and CO2 and H2O in the exhaust gas flowed out from the cooler 10 are removed by an adsorbing apparatus. The whole or a part of the atmospheric gas flowed out from the adsorbing apparatus 11 is introduced into the heat exchanger 8 by a conduit 21 and the atmospheric gas flowed out from the heat exchanger 8 is supplied to an atmospheric furnace 23 by a supply pipe 24. By this method high quality atmospheric gas reduced in unburnt hydrocarbon or soot and the concn. of residual oxygen is obtained and the conservation of energy of the atmospheric furnace using the atmospheric gas can be achieved.