To heat a steel material without oxidizing and to efficiently heat a furnace by equipping a plurality of heat-storage type heating devices for supplying high temp. inert gas into a furnace and a plurality of gas burners for supplying combustion gas into the furnace and controlling so as to indepen dently supply the inert gas and the combustion gas.

The heating furnace 1 is provided with two sets of the regenerative type heating devices 2 composed of a gas burner 3, combustion chamber 4 and heat-storage body 5 and two sets of the gas burners 7 arranged on the wall surface of throat part 6 for introducing the high temp. inert gas supplied from each storage type heating device 2 into the heating furnace 1, piping for supplying the combustion gas, inert gas and air into the gas burners 3, 7, valves and a switching valve 41, control unit, etc. In this constitution, the high temp. inert gas alternately supplied from two sets of regenerative type heating devices 2 to heat the steel material 8 without oxidizing. Further, the combustion gas is alternately supplied from two sets of gas burners 7 and the heating at the heat-up time etc., in the furnace which is unnecessary to non- oxidizing heating, is efficiently executed.